I can’t pair my watch, because it is with a different email address. How do I change it to my new email address?

How to remove Activation Lock

And if you bought this watch from somebody then;

The person that you bought/got this watch from needs to follow all the steps on this page;

Remove the Activation Lock so that the buyer can use it.

If they can't or won't then get your money back or recycle the watch and mark it down as a bad experience.

Neither the users on this forum or Apple can help you,only the original owner can help you.

Do you still have access to the original icloud account you were using?

Did you change the email address associated with your icloud account or did you create an entirely new icloud account with a different email address?

You need to turn off the activation lock on the watch. See this document: What to do before you sell, give away or trade in your Apple Watch, or buy one from someone else – Apple Support (AU)

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

Remove the Activation Lock Here.

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 with the serial number 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.

Is the Apple ID it is currently locked to yours or someone else’s?

Only the owner of the account it is locked to can remove the lock.