here are the steps on how to replace the back glass of an iPhone 13 Pro Max:

1. Gather your tools. You will need a heat gun, suction cup, pry tool, Phillips head screwdriver, and replacement back glass.Opens in 
2. Heat up the back glass. Use the heat gun to heat up the back glass until it is hot to the touch. This will make it easier to remove the old back glass.
3. Pry up the back glass. Use the suction cup to create a seal on the back glass. Then, use the pry tool to pry up the edge of the back glass.
4. Remove the old back glass. Once you have pried up the edge of the back glass, you can remove the rest of it. Be careful not to damage the internal components of the iPhone.
5. Install the new back glass. Clean the back of the iPhone with isopropyl alcohol. Then, align the new back glass and press it into place.
6. Screw in the screws. Use the Phillips head screwdriver to screw in the screws that hold the back glass in place.
7. Test your iPhone. Turn on your iPhone and make sure that it is working properly.

Here are some additional tips:

• Be careful not to heat the back glass too much, or you could damage the internal components of the iPhone.
• If the old back glass is cracked, be careful not to cut yourself on the glass shards.
• Make sure that the new back glass is aligned properly before you press it into place.
• If you are not comfortable replacing the back glass yourself, you can take your iPhone to a repair shop.