I bought an Apple Watch that is locked to another account.

Activation lock is a theft deterrent system, one of the best theft deterrent systems out there. You will need to contact the original owner. If you cannot reach them, you cannot use the watch

https://discussions.apple.com/docs/DOC-250001038?commentId=250004101025

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.