Screen popped off on its own

Typically I don’t see the glue holding screens on let go unless they have been left somewhere extremely hot. More often than not I see this cause by battery expansion which can be a fire risk. If the battery is even slightly swollen then replace it asap, then re-seal the screen. If the battery is not swollen and you see nothing abnormal, you can try putting new adhesive on and sealing it again, it is very rare but not unheard of for the stuff to just let go after a while (typically due to heat cycles).