My apple watch is not pairing with the new iphone. i don't know old icloud password

My apple watch is not pairing with the new iphone. I don't know the old icloud password. How can I pair my watch to the new phone? Since my phone is iPhone 7, I paired it to my friend's phone to use when I got my watch, so she doesn't know the icould password, I can't connect it to the new iPhone.