From the main menu, choose whatever accessory you are gonna use, either the kinect or controller. Select your character or make a new one. Choose "It's me!" and then choose yes if you're ready and that will bring you to another menu screen with "My Character & Settings". Choose that, then choose "Options" and then "Credits". Now, as the other solution said, it's kinda glitchy and you may not have to watch them to the end. I first watched mine all the way through and nothing popped so I went back into the credits 2 more times, and backed out almost immediately and the achievement popped. So I'd say if you can't get the achievement to pop first by backing in and out of the credits while it rolls the first 5 or so names, then try and watching it all the way through again.