Hello.

If you have already purchased reservations for the Bernina Express, than you don't need to do it again? Or am I missing something here?

You train ticket is the Interrail or Eurail Global Pass. You need a reservation for the panoramic cars.

I don’t understand the requirements hence asking. Yes, I have already purchased seat reservations. If that is all is required for global pass holder, then great. 
 

Thank you.

Perfect! Have a nice trip with the bernina express.

Don't forget to add the trip in the pass (app) or write it the paper pass.