you need to separate the two pieces of the backplate (the whole thing that's holding the wings, shoulder hinges and the swingbar) by unscrewing the 3 screws located on the inside of said backplate. two of the screws are the ones holding the left and right wings and covered by the shoulder hinges when positioned in battroid mode... the third screw is the one holding the swingbar. after you've removed these screws, the two pieces comprising the backplate will come apart and you can access the screw holding the shoulder hinge to the backplate.