help, new problem: can;t get the ground glass back on the camera.

I think is something I'm just going to have to get my teacher to help
me with, only now I've got the same problem about meeting the
homework deadline.

I can't figure out how to get it back on the camera. I did't really
mean to take it off in the first pace. I was trying to get the
viewfinder off the ground glass, and inadvertently took the
glass off with it.

It's probably stupidly simple, but I am not getting it. I can get
the hooks back into the slots, but I can't get the glass back to
lay flat on the camera at all.