*Take off a center cap and unscrew a screw most of the way. There is some hardware underneath the screw so don't take the screw out all of the way*
If the unsolvable state is just a single corner that is twisted in place, then you don't need to disassemble it. Once the layer is loose, you can rotate the layer 45 degrees and then twist the corner with your hand. Tighten your cube back up and you should be ready to go.