Apple Watch series 3

My cousin gave me his old Apple Watch series 3 since he got a series 7, he told me he removed it from the his cloud yet the screen on the watch won’t change unless I try to pair the device. It allowed me to pair and then my iPhone says the watch needs to be updated, I’ll update the watch and my phone tells me that the watch is up to date but the same screen will keep popping up. I got an iPhone 13 pro max, please help me.