Apple watch

i recently bought an Apple Watch from someone and when I first got it everything was signed out and ready to use. After awhile I decided to sign out and erase everything and restart it. My boyfriend wanted to use it so he tried to pair it to his phone and now it’s saying it’s locked. He can’t put no info because it needs the previous owner ( which is the person I bought it from) Apple ID. I tried to ask the guy I bought it for if he can please meet me to take his Apple ID off but he no longer answers. How do I solve this problem?! Please help.