Series 5 Apple Watch not connecting or updating

I was gifted a Series 5 Apple Watch. The previous owner couldn't get it to update due to not having wifi. I have been successful enough to update it to watchOS 6, then I had to do another update to watchOS 10.6.1 which kept sitting on preparing. Two days later, I have gone to update it again, and it has disconnected, and now I have to update it to watchOS 6 again, which is fine. But when I try to connect the watch it searches for an update, and then unpairs?? Any suggestions?