Turn the printed circuit board over, and remove two Torx T6 screws in the top corners holding the trigger mounts in place.

If you do NOT see some rectangular plastic piece resting on the bumper button on the printed circuit board, your controller's bumper is likely broken.

Once the screws are removed, we should have:

the printed circuit board,

trigger mounts,

and the top bar assembly holding the micro USB charging pre-drilled hole and outside bumper buttons. These are technically two pieces, but they sandwich together easily at four square points in the middle.