I don't know who previously had this apple watch so I can not contact them. Can you help me unlock it?

The person that you bought this watch from needs to follow all the rules 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.

If you cannot reach the previous owner of this Watch to help unlock the watch, then this Watch is completely useless to you.

You'll never get this Watch to ever work for you.

No one here can help you. Apple WILL NOT help you.

Please recycle this device responsibly.

Next time, purchase an Watch directly from Apple or from other legitimate, more trusted retail sources, either locally or online.

Sorry & Best of Luck to You!