Here is .cmp 

<aura:component controller="PickListHandler" implements="force:appHostable,flexipage:availableForAllPageTypes,flexipage:availableForRecordHome,force:hasRecordId,forceCommunity:availableForAllPageTypes,force:lightningQuickAction,lightning:actionOverride" access="global" >
    <!-- Actions-->
    <aura:handler name="init" value="{!this}" action="{!c.doInit}" />
    <aura:handler event="force:refreshView" action="{!c.isRefreshed}" />
  
    <!-- variable-->
    <aura:attribute name="lstLevel1" type="String[]" />
     <aura:attribute name="lstLevel2" type="String[]"  />
      <aura:attribute name="lstL3"  type="String[]"  />
        <aura:attribute name="firstlevel1selected" type="String" default="" />
     <aura:attribute name="secondlevelselected" type="String" default="" />
      <aura:attribute name="thirdlevelselected"  type="String" default="" />
    
	   <div class="slds-container--center slds-container--small slds-m-top--small">
        <div class="slds-form--stacked">
             
            <lightning:select name="parentPicklist" label="Level 1"  aura:id="ddLevel1"  onchange="{!c.getLvl1}">
                <option value="">--- None ---</option>
                <aura:iteration items="{!v.lstLevel1}" var="item1">
                    <option  value="{!item1.value}" selected="{!item1.selected}" >{!item1}</option>
                </aura:iteration>
            </lightning:select>
             
            <lightning:select name="Level2Picklist" label="Level 2"  aura:id="ddLevel2"   onchange="{!c.getSelectedValue}" >
                <option value="">--- None ---</option>
                <aura:iteration items="{!v.lstLevel2}" var="item2">
                    <option  value="{!item2.value}" selected="{!item2.selected}" >{!item2}</option>
                </aura:iteration>
            </lightning:select>
			
			 <lightning:select name="Level3Picklist" label="Level 3"  aura:id="ddLevel3" onchange="{!c.getlevel3}"  >
                <option value="">--- None ---</option>
                <aura:iteration items="{!v.lstL3}" var="item3">
                    <option  value="{!item3.value}" selected="{!item3.selected}" >{!item3}</option>
                </aura:iteration>
            </lightning:select>
             
        </div>        
    </div>
   <lightning:button variant="brand" label="Save" onclick="{!c.onConfirm}" />
</aura:component>

here is controllerJS
 

({
  
    doInit : function(component, event, helper) {
        var action = component.get("c.getLevel1");
        action.setCallback(this, function(e) {
            if(e.getState()=='SUCCESS'){
                var result=e.getReturnValue();
                component.set("v.lstLevel1",result);
            }
        });
        $A.enqueueAction(action);
    },    
    getLvl1:function(component, event, helper){
       
        var picklist=component.find('ddLevel1');
        var picklistvalue=picklist.get('v.value');
        component.set("v.firstlevel1selected",picklistvalue);
        var action = component.get("c.getLevel2");
        action.setParams({  'strName' : picklistvalue  });
        action.setCallback(this, function(e) {
            if(e.getState()=='SUCCESS'){
                var result=e.getReturnValue();
                component.set("v.lstLevel2",result);
                helper.getSelectedValue(component,event,helper);
            }
        });
        $A.enqueueAction(action);
      
            },
    getSelectedValue:function(component, event, helper){
        var picklist=component.find('ddLevel1');
       
        var picklistvalue=picklist.get('v.value');
         
        var picklistdep=component.find('ddLevel2');
        
        var picklistvaluedep2=picklistdep.get('v.value');
        component.set("v.secondlevelselected",picklistvaluedep2);
        var action = component.get("c.getLevel3");
        
        action.setParams({  'strName1' : picklistvalue,
                         'strName2' : picklistvaluedep2});//
        action.setCallback(this, function(e) {
            if(e.getState()=='SUCCESS'){
                var result=e.getReturnValue();
                component.set("v.lstL3",result);
            }
        });
        $A.enqueueAction(action);
    },
    getlevel3:function(component, event, helper){
        var picklist=component.find('ddLevel3');
       
        var picklistvalue=picklist.get('v.value');
         component.set("v.thirdlevelselected",picklistvalue);
        
    },
    onConfirm:function(component, event, helper){
        var picklist=component.find('ddLevel1');
        var picklistvalue=picklist.get('v.value');
        var picklistdep=component.find('ddLevel2');
        var picklistvaluedep2=picklistdep.get('v.value');
       
        var picklistdep3=component.find('ddLevel3');
        var picklistvaluedep3=picklistdep3.get('v.value');
              
        var action = component.get("c.savecasetype");
        
        action.setParams({  'level1' : picklistvalue,
                          'level2' : component.get('v.secondlevelselected'),
                          'level3' : component.get('v.thirdlevelselected'),
                          'id' : component.get("v.recordId")});
                          
        
        var toastEvent = $A.get("e.force:showToast");
        action.setCallback(this, function(e) {
            if(e.getState()=='SUCCESS'){
                var result=e.getReturnValue();
                if(result==='successfull'){
                    toastEvent.setParams({
                        "title": "Success!",
                        "message": "The record has been inserted  successfully."
                    });
                    toastEvent.fire();
                }else{
                    toastEvent.setParams({
                        "title": "Error",
                        "message": "The record has not been inserted  successfully."
                    });
                    toastEvent.fire();
                }
            }
            $A.get('e.force:refreshView').fire(); 
        });
        $A.enqueueAction(action);
       
    },
      /*page refresh after data save*/    
      isRefreshed: function(component, event, helper) {
        location.reload();
    }
       
       
})

Now I want to extend the functionality of above lightning component so that user who wishes to change Record data on Case can just update the value of Level1, Level2 and Level3 and do an Upsert on the same case
Now to achieve Edit a record functionality,added lightning:actionOverride in apex cmp and then overridden the standard Edit button of ERT case type custom object ..Here comes the problem when I use the same component in Edit button ,I see error as below

Hence  I need help to  write a  code to load an existing record and modify it