Apple Watch activation password required

You will not be able to unlock this Apple Watch without the original owner removing the lock.

You should contact the seller and try to get it removed. They should've followed this support page: What to do before you sell, give away, or trade in your Apple Watch, or buy one from someone else - Apple Support.

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.