If I purchased a Apple Watch second hand and the person doesn’t remover the activation code what do I do?

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.

You need to get in touch with the previous owner of the Watch, otherwise, the Watch is of no use to you. You should ask them for a refund.

About Activation Lock on your Apple Watch – Apple Support