Help with mouse's internal movement tracking mechanism?

Hello everyone.

I own a Blackweb BWG66 gaming mouse that recently stopped registering my movements entirely and I know it’s a hardware issue. I was able to open up the mouse but this is my first time ever opening a gaming mouse and I’d love to have assistance while I attempt to fix it.

Every button works, it’s just the internal movement sensor that seems to have malfunctioned. I can provide pictures if needed.

The earlier I get this fixed, the faster I get back to practicing my aim :)

EDIT: So I found the issue, the red light was unaligned and I tilted it back into position. Wouldn’t you know it, it works again! But with a problem solved comes another. While I reassembled the mouse, I noticed that mouse buttons 2, 4 and 5 are stuck and will not press down correctly. There is also this mystery metal piece that came out, which I’m not certain as to what its purpose is. Will post pictures in the second edit.