It's odd but not unheard of for the adhesive holding the screen onto the frame to fail; I'd suggest making sure the frame isn't bent and that' the reason the screen came off. If it's okay, then it should be relatively straight-forward to simply reglue the screen back onto the frame. You'll need some adhesive; something like B-7000 should work fine, or whatever you can get - for example the E-6000 glue iFixit sells would be suitable.
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It's odd but not unheard of for the adhesive holding the screen onto the frame to fail; I'd suggest making sure the frame isn't bent and that's the reason the screen came off. If it's okay, then it should be relatively straight-forward to simply reglue the screen back onto the frame. You'll need some adhesive; something like B-7000 should work fine, or whatever you can get - for example the E-6000 glue iFixit sells would be suitable.
Although you can probably reglue the screen without completely removing it from the phone, I'd suggest following this video and taking it all the way off so you can do a thorough job cleaning the old adhesive to ensure a good grip for the new glue.
It's odd but not unheard of for the adhesive holding the screen onto the frame to fail; I'd suggest making sure the frame isn't bent and that' the reason the screen came off. If it's okay, then it should be relatively straight-forward to simply reglue the screen back onto the frame. You'll need some adhesive; something like B-7000 should work fine, or whatever you can get - for example the E-6000 glue iFixit sells would be suitable.
[product|IF145-413|E6000 Adhesive Glue|new_window=true]
Although you can probably reglue the screen without completely removing it from the phone, I'd suggest following this video and taking it all the way off so you can do a thorough job cleaning the old adhesive to ensure a good grip for the new glue.
[link|https://www.youtube.com/watch?v=Uym4ghSYh8g|Redmi 9 Lcd Replacement|new_window=true]
Hopefully that's all you'll need to do to fix your loose screen! Let us know how it all turns out.