Use a Torx T6 screwdriver to remove the three screws inside the back cover, and the four screws around the handles.

If you never opened the controller before, the screws are hidden underneath the sticker. Either cleanly remove the sticker using Goo-Gone, or punch through the sticker with the screwdriver or a thin blade at these locations to expose the pre-drilled holes.

In my experience, the top two screws only need to be loosened as the sticker residue will hole them in the long shafts. The rest can be completely removed and put to the side.