To fix this issue take a hard flat tool, a metal pry tool works well for this and pry up on the bent piece. If your battery door had issues popping open you can give the round bend piece (photo 3) the same treatment but don't put as much force as you could damage it.

Once it is raised a bit put the mouse back together to see if it works again or needs further prying. If there are still issues after a few bending attempts try cleaning the chassis side button and make sure it is pressing in. (photo 3, step 4)