Syncing Apple Watch with new iPhone and different email accounts

I just purchased a new phone. My watch will pair with it but won’t sync. I do not have the old Yahoo password that the watch was set up under. I have changed all my passwords and reset the watch completely but nothing has helped. My watch is under yahoo and my phone is iCloud. I was told they are not talking to each other. Can anyone help?

[Re-Titled by Moderator]

Original Title: Apple Watch issues