The screen is glued to a plastic frame which is then clipped into the frame.
I’m assuming the glue came undone, but if you could post a picture it would be helpfull to tell.
Profesionally speaking, the screen should be replaced if the glue is done, but you could apply a small amount of grazy glue as well and hold the screen in place while it dries. It should hold for a while.
Less is more in this case, only place a very small amount so you don’t glues things that are not suposed to be glued togerther.
I hope this helps