Piece of the L1 bumper component fell off

So I have an Astro CR-40 which I got as a gift. I dropped the controller on the bumper and the button stopped working. I opened up the controller to find that a piece of meta had fallen out

. The piece of metal moves around too much to go back into the same place and may be damaged. Comparison with the other working side.

.

Anyone know what the piece is called and where I can get a replacement? Any recommendations on how to repair as well.