Although nobody makes a guide showing just how to replace the rear glass of your phone, pretty much every guide made starts out with that as the very first step, so really all you have to do is follow the first step and you're done. Here's one from the Spanish site Nadie Me Llama Gallina for replacing the battery.
Manuals / OnePlus 10T / Battery - Nobody Calls Me Chicken
As I mentioned, all you have to do is follow the first step. You can find replacement parts on all the major sites like Amazon, eBay and AliExpress, and many others. Here's one that came up on my cursory search, but you'll have to select a color to match your phone, although any color will work.
Amazon.com: Ubrokeifixit for OnePlus 10T 6.7" Rear Back Glass Door Cover Replacement for OnePlus 10T 6.7" CPH2415 CPH2413 CPH2417 2022 (10T Green) : Cell Phones & Accessories
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