Apple watch keeps restarting and can’t get into the system

Here is how this happened:

I unpaired my apple watch and then removed it from my account. (I was trying to reset my apple watch because I cannot update the system for some reason and I was locked out of the watch app on my iPhone. The watch app said “need update”. I was running on watchOS 9.1 and it asked me to update to watchOS 9.6 btw) It looks that apple watch was still processing my data after I unpaired it (it should erase my data from itself) but I removed it from my account so quickly that the apple watch seemed to break its own system.

Now, apple watch keeps restarting (loop through apple logo and black screen). I took it to apple repair but they said they cannot get into the recovery system because apple watch kept restarting.

I tried pressing two buttons to force restart, but it wouldn’t work. Apple support suggested that I could take it to third-party repair, because they would charge me 2300RMB(~300 USD) if they send it to factory.

By the way, the battery will run out after 2 hours without charging and it is heating up itself on a charger right now. I have looked through other posts(S3, S4 keeps restarting), but every solution in the comment section didn’t solve my problem. If you have the same problem, please reply with what you did so that apple can potentially fix this.