@charuDutt ,thanks for your reply , my requirement is need to assign  permissionsetA when user record is inserted with roleA and when user record updates with roleB need to assign permissionsetB this is achieved sucessfully, now when i change roleA to roleB need to delete permissionsetA and add permissionsetB and vice versa , am getting below error when trying to change role in user record

Error: Invalid Data.
Review all error messages below to correct your data.
Apex trigger assigningpermission caused an unexpected exception, contact your administrator: assigningpermission: execution of AfterUpdate caused by: System.DmlException: Insert failed. First exception on row 0; first error: DUPLICATE_VALUE, Duplicate PermissionSetAssignment. Assignee: 0052v00000hRRwk; Permission Set: 0PS2v000006IUrs: [AssigneeId, PermissionSetId]: Trigger.assigningpermission: line 10, column 1


mytrigger:

trigger assigningpermission on User (after insert,after update,before delete,after delete) {
user us = [select id, UserroleId from user where id in :trigger.new];
  PermissionSet ps =  [SELECT Id FROM PermissionSet
                         WHERE Id = '0PS2v000006IUrsGAG'];
    PermissionSet ps1=[select Id from permissionset where Id='0PS2v000006IUrxGAG'];
    //RoleA id
      if(us.UserroleId == '00E2v000002SZA7' ){                 

PermissionSetAssignment psa = new PermissionSetAssignment(PermissionSetId = ps.id, AssigneeId = us.id);
 insert psa;
         
      system.debug(psa.AssigneeId);     
    }
    //roleB id
    if(us.UserRoleId=='00E2v000002SZAC'){
      PermissionSetAssignment psa1 = new PermissionSetAssignment(PermissionSetId = ps1.id, AssigneeId = us.id);
insert psa1;
    
    }
//deleting permissionset 
    Set<Id> usrId = new Set<Id>();
    for(User u :  trigger.new){
        if(u.UserRoleId != Trigger.oldMap.get(u.Id).UserRoleId){
           usrId.add(u.Id);
        }
    }
    list<PermissionSetAssignment> lstPerm = [SELECT Id, PermissionSetId, PermissionSetGroupId, AssigneeId, IsActive 
                                             FROM PermissionSetAssignment WHERE AssigneeId IN :usrId ];
    if(lstPerm.size()>0){
        delete lstPerm;
    }
    
}

Thanks in Advance