Remove activation lock without phone

My wife hasn't used her watch in a while. She recently got a new phone and I traded in the old one. I did not unpair it from the old phone because I has forgot she even had the watch. The new phonw is trying to pair with it but I don’t want to and it won’t anyway. I just want to reset the watch so I can trade it in. From what I read though it won’t remove the activation lock just by resetting.

So what do I do to remove it so it can be traded in?

thanks

eric