Locked PIN code from a list Apple Watch and trying to open it

my son who is 7 found an Apple Watch in a parking lot we were the only ones there when we pulled in and found it. Don’t know who or where the owner is and so I took it home with us and charged it up but there’s a PIN code on it so I can’t even get into it to even let the person know I found it .can anyone help me to get the watch to open ?