My Apple Watch has a different Id on it and I can’t pair it with my new one or change it

You can ask apple to remove the activation lock online on this page;

Online Activation Lock Removal Tool.

Or this;

If you can't remember/gain access to the apple id that paired the watch to the phone.Take the watch and it's receipt along with some photo id and any other proof of ownership to an Apple Store and request that they remove the Activation Lock for you.

Why is the ID different. Is this not your Watch, or is this a used Watch that you just purchased from someone? Did they not wipe and prepare the Watch for a new owner?