Insert the flat edge of a metal spudger in the seam between the adapter body and the plastic casing. Move the spudger into one of the corners.
Push down on the spudger to separate the casing from the adapter until you hear a click and the casing stays open on that side.
Do the same to the other side until the casing comes off.
When reassembling, first align the headphone jack in the back of the adapter body with the hole in the casing, then align the tabs on the floor of the casing with the holes in the bottom of the adapter body.
Remove three 5.0 mm T5 Security Torx screws along the edges of the controller housing.
Remove two 8.0 mm T5 Security Torx screws near the top-center of the adapter.
With your fingers, carefully lift the adapter housing from the button panel.
Be careful not to yank the wires connecting the two halves of the circuit board.
Pull back on the controller USB connector with your finger to separate the main adapter circuit board from the rubber mold in the button panel.
With your fingers, partially peel back the rubber molding near the button you want to replace.
Do not rip the rubber mold. The mold will need to be used for the new button, and it must remain intact in order for the button to work properly.
Using the straight, pointed end of a small pointed spudger, scrape off the glue between the plastic button and the rubber mold.
Grip the plastic tabs on either side of the button with tweezers.
Squeeze the tweezers to pop the button out the front face of the button panel.