Thanks Bharagavi  your code helped me to fix the issue I modified little bit to make it work below is the working code. 
 
I need your help in building test class to get 75+ code coverage 
 

Trigger updateprimarycampaign on Opportunity (Before Update ,After insert)
{
    Set<Id> ConIds=new Set<Id>();
    Set<datetime> OpCreateddate = new set<datetime>();
    Set<id> setoppId=new set<id>();
 if ( checkRecursive_updateprimarycampaign.runOnce()) 
 {
    if(Trigger.isUpdate)
    {
   
     for (Opportunity op : Trigger.new) 
            {
            ConIds.add(op.contact__c);
            OpCreateddate.add(op.createddate);
            }
     List<CampaignMember> cmList = new List<CampaignMember>([SELECT id,CampaignId,ContactId FROM CampaignMember 
                                     where ContactId in: ConIds and HasResponded = true and 
                                           CreatedDate <= :OpCreateddate]);
       Map<Id,Id> camCon=new Map<Id,Id>();
       for(CampaignMember cm:cmList)
       {
       camCon.put(cm.ContactId,cm.CampaignId);
       }
       for(Opportunity op : Trigger.new)
       {
         if(camCon.containsKey(op.Contact__c))
         {
         op.CampaignId=camCon.get(op.Contact__c);
         }
         else
         op.CampaignId=null;
       }
    }
    else if (Trigger.isInsert)
    {
     List<Opportunity> lstOppToUpdate = new List<Opportunity>();
      for(Opportunity opp: Trigger.new ) 
        {
            setoppId.add(opp.id);
            OpCreateddate.add(opp.createddate);
        }
     
        List<Opportunity> lstOpp = [select id , CampaignId,Contact__c from Opportunity where id in :setoppId ];
        Set<Id> ConIds=new Set<Id>();
     for (Opportunity op : lstOpp) 
            {
            ConIds.add(op.contact__c);
            }
     List<CampaignMember> cmList = new List<CampaignMember>([SELECT id,CampaignId,ContactId FROM CampaignMember 
                                     where ContactId in: ConIds and HasResponded = true and 
                                           CreatedDate<=:OpCreateddate]);
       Map<Id,Id> camCon=new Map<Id,Id>();
       for(CampaignMember cm:cmList)
       {
       camCon.put(cm.ContactId,cm.CampaignId);
       }
       for(Opportunity op : lstOpp)
       {
         if(camCon.containsKey(op.Contact__c))
         {
         op.CampaignId=camCon.get(op.Contact__c);
         lstOppToUpdate.add(op);
         }
         else
         {
         op.CampaignId=null;
         lstOppToUpdate.add(op);
       }
       
       }
        if(lstOppToUpdate.size() > 0 )
            {
                update lstOppToUpdate;
            }
        
    }
 }
}

 Below is the old test class which is giving 62% code coverage. need your suggestion to improve the coverage. 

@isTest(SeeAllData = true)
public class test_updateprimarycampaign{
    static testMethod void TestCampaignMember (){

        Test.startTest();
        
        Account testAcc = new Account (Name = 'Test Account 2342343', Email_Domain__c = 'sudhir1231@samarth.com');
       {
        insert testAcc;
        }

        //Creates Contact to be linked to Campaign Member
        Contact testContact = new Contact(FirstName = 'TestContactF245634', LastName = 'TestContactL', Email = 'none@navinet.net',accountid=testAcc.Id,LeadSource = 'Community' );
        insert testContact;
        
        Campaign cp =  [SELECT Id FROM Campaign LIMIT 1];
        
        Opportunity testOpp = new Opportunity (Name = 'Test Name 987191',                       
                                     AccountId = testAcc.Id,
                                     Type = 'New Customer',                                   
                                     StageName = 'Open',
                                     Amount = 50000.00,
                                     CloseDate = System.today(),
                                     LeadSource = 'Community'
                                     );
    {
    insert testOpp;
   }

        //Creates a new campaign memeber, associaites it with 1 provider sales campaign, and inserts
        CampaignMember newMember = 
        new CampaignMember(ContactId = testContact.id, status='Sent', campaignid = cp.id);
        insert newMember;

       Opportunity opp1a = [SELECT Id,campaignid 
                            FROM Opportunity
                            WHERE Id = :testOpp.Id];

        opp1a.campaignid = cp.id;
        
        update opp1a;

        Test.stopTest();

    }
}

Thanks
Sudhir