Left bumper unresponsive (including the small grey button behind it)

After a drop, the left bumper button was clearly damaged (the long flexible arm was broken) and the button was unresponsive.

However after opening up the case and popping off the bumper plastic, I couldn't get the small grey trigger button behind it to respond at all to presses, despite seemingly being well attached to the board.

I would just replace the entire board and buttons, but that board doesn't seem to be something iFixit sells.

Looking for suggestions on how to proceed.

Thanks!

... oh, and the left trigger still works fine, if this helps narrow anything down - I thought maybe the small grey button behind the bumper had soldering that broke loose although it's hard to see much and I was hesitant to take anything further apart without consulting with folks who might know more - maybe there's a guide to safely disassembling what's left of the that mechanism and a picture of what a normal one should look like, for example.