I bought a locked watch how can I unlock it

If you can't reach the person you bought the watch from or they can't remove activation lock, you have purchased a totally useless watch, you will never be able to use. Apple will not help you. We cannot help you. If this becomes your reality, either get your money back or recycle the watch responsibly.

Read this --> The All Too Common SAD Reality of Buying … - Apple Community

Barrysedge3681 wrote:

I bought a used apple 3 watch and it is locked how do I unlock it

Contact the person you bought the device from and have them remove the icloud activation lock, the is the only way to unlock it.

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

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.