I am not certain I follow you. You pick a random robot and ask "Which door would the other robot say is the safe door?" If you have picked the truth telling robot, he will point to the death door (assuming he knows the other robot always lies). If you picked the lying robot, then he would also point to the death door (because he knows that the truth telling robot would point to the safe door and so he lies and point to the death door). Either way you go through the other door.