I want to replace my back camera

Hi Kuldeep,

It doesn't appear that you can replace the rear cameras individually; rather it looks like they come as an assembly of all three and get replaced as a single unit. You have to remove the motherboard to get to them, but on your phone it's actually not too bad of a job. Sorry to say that iFixit doesn't have a guide for you, but there's a Spanish site called Nadie Me Llama Gallina that has exactly what you need.

Manuales / OnePlus 7T / Rear cameras

The cameras themselves seem to be fairly easy to come by; take a look on places like Amazon, eBay and AliExpress for starters; you can undoubtedly find them in several other places as well. Here's an example of one of the first ones that came. up on my cursory search.

Original Front Back Camera For OnePlus 7 Pro One Plus 7T Backside Frontal Facing Rear Selfie Camera Module Repair Spare Parts - AliExpress

Good luck; let us know how it goes!