The right trigger is on your left-hand side when working on the Steam Deck OLED, as it's laying upside down.

The trigger clips into place on two pegs on the frame, which double as the hinge.

Place the flat end of a spudger onto the inside edge of the trigger's right clip.

Use your fingers to push the trigger toward the right as you wedge the spudger between the clip and the peg.

Use your spudger to pivot the trigger clip out, away, and up from the peg to unlatch it.

During reassembly, latch the left peg first. Once in place, push down on the trigger to latch the right peg, producing an audible "click" sound.

Check to make sure that the trigger spring is properly aligned. Test the trigger action before continuing reassembly.