How can you unlock your Apple Watch from a iCloud?

I was using another iPhone when I got my Apple Watch but I didn’t know that you had to disconnect your Apple Watch when you got a new phone so now I can’t get into my Apple Watch? What do I do? I got a new phone and I can’t use the email I have on this phone because it’s not the same as the one that wasn’t on my other phone and I don’t remember the other iCloud?..