Prepare the paper clip spring compressor (optional) by unbending the end of a paper clip 90º.

With needle-nose pliers, grab about 1/8" (red) of the end in your dominant hand. Further below, use channel lock or vice grip pliers (with a wider face) to stabilize (blue).

Holding the channel lock (blue) pliers in place, bend the end in half (90º) and then in half again. Then, use the flat part of the needle-nose pliers to compress this fold unto a tight U-bend.

As shown in the second photo (but prior to reinstalling the housing to the logic board to avoid damaging), compress the spring with the left side of the arm clipped in place, but the right side not yet clipped in. Once the spring is compressed, the paper clip is thin enough that you can click the other side of the arm into place.

The small bend in the arm must sit entirely on top of the spring.