I have a link on my opportunity line item that users click to create a case for a specific team. Currently, the case record type creates as the default record type which is "Sales Support", however these need to override the default assignment rules and create a "Feasibility" case.
We had a developer create this who is no longer with us. There is a controller and visualforce page.
This is what I have:

Visualforce page:

<apex:page standardController="Case" extensions="FeasibilityRequestCaseController">
<script language="javascript">
   window.onload = new function() 
   { 
      // bring popup window to front
      window.focus(); 
      var ele=document.getElementById('{!$Component.form.block.section.olilookupid}');
      if (ele)
      {
         ele.focus();
      }
       
      var ele1=winMain.document.getElementById('{!$CurrentPage.parameters.olilookupid}');
      ele1.value=olilookupid;
       
   }
   
   function fillIn(addressField, olilookupid)
   {
      var winMain=window.opener;
      if (null==winMain)
      {
         winMain=window.parent.opener;
      }
      var ele=winMain.document.getElementById('{!$CurrentPage.parameters.olilookupid}');
      ele.value=olilookupid;

      var ele1=winMain.document.getElementById('{!$CurrentPage.parameters.olilookupid}');
      ele1.value=olilookupid;
               
      CloseWindow();
   }

   function CloseWindow()
   {
      alert('Thanks for raising new case for feasibility request. Feasibilty analysis personnel will update available feasibility options for you shortly.');
      var winMain=window.opener;
      if (null==winMain)
      {
         winMain=window.parent.opener;
      }
      winMain.closeLookupPopup();
   }
</script>    
    
    
<apex:pageBlock >
<apex:pageBlockSection title="Raise a New Case - Request Feasibility Analysis" columns="1" showHeader="True" collapsible="False">
</apex:pageBlockSection>
</apex:pageBlock>
<apex:form >
<apex:pageBlock title="Feasibility Request - Case Information" >
<apex:pageBlockButtons >
    <apex:commandButton action="{!save}" value="Submit for Feasibility Analysis" oncomplete="CloseWindow();"/>
</apex:pageBlockButtons>
    <apex:pageBlockSection >
    <apex:inputField value="{!frc.Subject}" style="width: 360px;"/>        
    <apex:inputField value="{!frc.Opportunity__c}"/>
    <apex:inputField value="{!frc.Reason}"/>
    <apex:inputField value="{!frc.Status}"/>
    <apex:inputField value="{!frc.Description}" style="width: 360px; height: 40px"/>
    <apex:inputField value="{!frc.Origin}"/>
    <!--<apex:inputField value="{!frc.RecordType.Name}"/>-->
</apex:pageBlockSection>
</apex:pageBlock>
</apex:form>
</apex:page>


Controller:
public class FeasibilityRequestCaseController {
    public String oliID{get; set;}
    public String olilookupid{get; set;}
    public Case frc{get; set;}
    public String address{get; set;}
    
public FeasibilityRequestCaseController (ApexPages.StandardController controller) {
        String oliId = ApexPages.currentPage().getParameters().get('oliIDForNewCase');
        String olilookupid = ApexPages.currentPage().getParameters().get('olilookupid');
        String caseName = '';
        String caseAddress = '';
        opportunitylineitem oli;
        Id oppId;
        Id oppLIId;
        //oliId = '\'' + oliId + '\'';

        System.debug('FeasibilityRequestCaseController:: oliId - ' + oliId + ' :: olilookupid - ' + olilookupid);
        System.debug('Query:: Select id, name, Address_AEnd__c, OpportunityId from opportunitylineitem where id = ' + olilookupid);
    
        if(olilookupid!=null){    
        oli = [Select id, name, Address_AEnd__c, OpportunityId from opportunitylineitem where id = :olilookupid];
                caseName = oli.Name;
                caseAddress = oli.Address_AEnd__c;
                oppId = oli.OpportunityId;
                oppLIId = oli.Id;
        }
        
        // RecordType recordType = [Select Id From RecordType  Where SobjectType = 'Case' and Name = 'NZ Feasibility'];
    
        frc = new Case();    
        frc.Subject='New Feasibility Request: ' + olilookupid;
        frc.Reason='Supplier quote request';
        frc.Status='Open';    
        frc.Origin='Opportunity';
        frc.Description='Please provide feasibility for Address: ' + oliId;
        // frc.RecordType=recordType;
        frc.isBEnd__c=false;
        //frc.Related_Product_del__C = oppLIId;
        frc.oliid__c=olilookupid;
        if(oppId!=null) frc.Opportunity__c= oppId;
    }

public pagereference Save()
    {
        insert frc;
        Case c = [select Casenumber from Case where id=:frc.id];
        system.debug('New Case Number: ' + c.Casenumber );
        return null;
    }
        
}