public class EmployeeRegistrationController 
{
    public String selectedTab{get; set;}
    public EmpID__c EmpID{get;set;}
    public EmployeeInfo__c EmpDetail{get; set;}
    public EducationInfo__c EduDetail{get; set;}
    public List<EducationInfo__c> listEducation {get; set;}
    public TechnologyInfo__c TechDetail{get;set;}
    public List<TechnologyInfo__c> listTechnology {get;set;}
    public List<EducationInfo__c> listEduInsert {get; set;}
    public List<TechnologyInfo__c> listTechInsert{get;set;}
    public Boolean button{get;set;}
    public Boolean btnSubmit{get;set;}
    public Boolean btnSave{get;set;}
 
    public EmployeeRegistrationController()
    {
        selectedTab='Employee';
        EmpDetail=new EmployeeInfo__c();
        listEducation=new List<EducationInfo__c>();
        TechDetail=new TechnologyInfo__c();
        listTechnology=new List<TechnologyInfo__c> ();
        EmpID=new EmpID__c();
        button=true;
        btnSubmit=true;
        btnSave=false;
    }
    
    public void goNext1()
    {
        selectedTab='Education';
    }
    
    public PageReference saveInfo()
    {
        if(EmpDetail.First_Name__c==null||EmpDetail.Last_Name__c==null||EmpDetail.Email__c==null)
        {
            ApexPages.Message msg=new ApexPages.Message(ApexPages.Severity.ERROR,'Please fill Basic details: First Name, Last Name, Email ID');
            ApexPages.addMessage(msg);
        }
        else
        {
        try
        {
            insert EmpDetail;
            ID Eid=[select ID from EmployeeInfo__c where Email__c=:EmpDetail.Email__c limit 1].ID;
            EmpID=new EmpID__c(Eid__c=Eid);
            button=false;
            btnSave=true;
        }
        catch(Exception e)
        {
            System.debug(e.getMessage());
        }
        }
        return null;
    }
    
    public void goNext2()
    {
        selectedTab='Technology';
    }
    
    public PageReference addNewRow()
    {
        if(EmpID.Eid__c==null)
        {
            ApexPages.Message msg=new ApexPages.Message(ApexPages.Severity.ERROR,'Please fill the Basic detail First');
            ApexPages.addMessage(msg);
        }
        else
        {
        EduDetail=new EducationInfo__c();
        EduDetail.Employee__c=EmpID.Eid__c;
        listEducation.add(EduDetail);
        }
        return null;
    }
    
    public PageReference saveEducation()
    {
        for (EducationInfo__c c:listEducation)
        {
        if(c.course__c==null)
        {
            ApexPages.Message msg=new ApexPages.Message(ApexPages.Severity.ERROR,'Please fill the details');
            ApexPages.addMessage(msg);
        }
        else
        {
            try
            {
                upsert listEducation;
                listEduInsert=[SELECT Name, course__c,From_Date__c,To_Date__c FROM EducationInfo__c WHERE Employee__c=:EmpID.Eid__c];
            }
            catch(Exception e)
            {
                System.debug(e.getMessage());
            }
        }
        }
        listEducation.clear();
        return null;
    }
    
    public PageReference addNewRow2()
    {
        TechDetail=new TechnologyInfo__c();
        TechDetail.Employee__c=EmpID.Eid__c;
        listTechnology.add(TechDetail);
        return null;
    }
    
    public PageReference saveTechnology()
    {
        for(TechnologyInfo__c t: listTechnology)
        {
        if(t.Skill__c==null)
        {
            System.debug(t.Skill__c);
            ApexPages.Message msg=new ApexPages.Message(ApexPages.Severity.ERROR,'Please fill the details');
            ApexPages.addMessage(msg);
            System.debug(msg);
        }
        else
        {
            try
            {
                upsert listTechnology;
                listTechInsert =[SELECT Name, Experience__c,Level__c,Skill__c FROM TechnologyInfo__c WHERE Employee__c=:EmpID.Eid__c];
                btnSubmit=false;
            }
            catch(Exception e)
            {
                System.debug(e.getMessage());
            }
        }
        }
        listTechnology.clear();
        return null;
    }
    
    public PageReference submit()
    {
        SentEmail.sentToAdmin(EmpID.Eid__c);
        SentEmail.sentToUser(EmpID.Eid__c);
        PageReference pageRefer=new PageReference('/apex/FinalPage');
        pageRefer.setRedirect(true);
        return pageRefer;
    }
}

Can someone please suggest me?