I bought a Apple Watch it’s locked and I don’t know the owner

The person that you bought this watch from needs to follow all the steps in this link;

Prepare the watch so the buyer can use it.

If they can't or won't then get your money back or recycle the watch and put it down to experience.

Recycle it or return it. It will not work for you unless the original owner removes activation lock.

https://support.apple.com/en-us/HT205009