How do I change my backglass and what glue do I use?

Hi,

Getting the back glass off requires a serious amount of heat. A repair shop will often use a laser machine to burn the glue underneath the glass. I've done a few glass replacements as hobby repairs and had to use a heat gun with adjustable heat (around 300C), and thin metal prying tools including a flat n17 X-acto knife.
For the glass around a camera, its best to use a spring loaded shatter tool, since there isn't really any other easy way to break glass that thick. To protect yourself from future issues, I'd like to advice to take out all the internals before starting this repair, It's very easy to rip flex cables or damage small components, since some parts are glued to the glass. Its a free world and we do what we want.
These repairs are never fun, and always take longer than planned.

That said:

My ultimate advice is to do a housing swap, prices have come down tremendously on housing replacements, and time to cost ratio for a glass only repair without laser machine is just terrible. You'll lose less time and your house won't be littered with glass.

Tips:
-Wear safety goggles when prying glass shards.
-Buy a new set of MagSafe magnets, these things have a mind of their own. You'll lose/break the old ones or forget their correct orientation.
-Use glue that remains flexible after drying, that way you might improve the durability of your phone. (B-8000-isch,...)
-Watch out for the LiDaR Filter, a replacement back glass, or even a housing might have a fake filter, it should look pink on the inside. If it's not, you should scratch off whatever is on the replacement and transfer over what's left on your original cracked glass. If you forget this, no LiDaR (who uses this anyway)

-Make sure your new glass fits, the metal might have deformed.
-If you opt for glass-only, buy the rubber O-rings that hold up the camera rings, and buy a glass that states to have 'Large Camera Holes' The original glass doesn't fit over the camera rings. (In the factory the camera lenses are spot welded AFTER the back glass is glued/cemented on)