Try this,
Go with your dog in room with door,close the door,exit from the room and close door,im pretty sure he'll try to open the door,if he fail to open it,try that 10x times so he can see and learn how you open the door.
Go with your dog in room with door,close the door,exit from the room and close door,im pretty sure he'll try to open the door,if he fail to open it,try that 10x times so he can see and learn how you open the door.