Hey Raveendar,

I hope you had a chance to look at other replies also. I am guessing your requirement is different and looking for switching in activity step.

Lets take example:

you want to swtich to app2, lets open the application object on a page "App2Page" by using obj-open. we need this page for next step.

Also get the accessgroup name of the application.

Use the following logic to swtich.

String targetAG = tools.getParamValue("AccessGroup"); // here input of accessgroup iam taking from paramer, in your case may be different       

try {
   PRThread prtRef = tools.getThread().getRequestor().getThread("STANDARD"); //switching in standard thread
   ((com.pega.pegarules.priv.authorization.PegaAuthorization)prtRef.getAuthorization()).setActiveAccessGroup(prtRef, targetAG,true);
} 
  catch(Exception ex){
    oLog.error("Unable to switch to user provided access group'" + targetAG + "'.Following exception is encountered:" + ex.getMessage());
  }

Above logic is for switching the application only. after swtiching you may have to set the thread context with the current application rulesets. so that you can access the rules of those rulesets in the standrad thread after switching. to set the ruleset context call the activity "Code-Security.pzSetRulesetsForThisApp" on the application page you have created above i.e "App2Page". this activity sets the ruleset context of switched application in standrad thread and do your logic after this step.

Note: As you are in 7.3.1 version, above code steps can be found at the activity "pzValidateInputs"of "Code-Pega-List", in step 18,21

Let me know if you face any issues while implementing this logic. As we are using this logic in many places, ideally it should work in your case also.