what if you don't know the apple id and password of the user who used to own your apple watch and you can't contact them?

so my mom gave me this used apple watch after a student in her school she works at never claimed it. I went into the Apple Watch and went to settings and erased all the content settings in it. When I went to try to pair it with my iPhone, it said I needed to type in the apple user id and password of the previous owner. I don't know the previous owner and can't contact them. Im assuming the previous owner has to erase the Apple Watch device from his icloud and find my iPhone app in order for me to use it with my own things. However, I have no way of contacting the original owner so how do I hook the Apple Watch up to my phone now?