I changed my Apple ID, but my Apple Watch will not sign in with my new Apple ID...What do I do???

If you have changed your ID, have you followed the steps in this article? Make sure you turn of Find My Phone before signing out of the old ID. Once signed out and Find My Phone is off, then sign in with the new ID, then turn Find My Phone back on.

What to do after you change your Apple ID or password - Apple Support.  *. 

See if anything here helps. 

Watch -  Set up your.    *

ASC YouTube for how to set up your Apple Watch

Watch - Unpair and erase your.   

Watch - pair with a new iPhone.    *

Watch isn't connected or paired with your iPhone.   *

Watch - If you can't pair an Apple Watch with your iPhone  *

ASC YouTube for how to unpair and reset your Apple Watch | Apple Support