How do I disconnect someone’s Apple ID from an apple watch

Follow this guide from Apple:

https://support.apple.com/en-us/HT208855

Bellarose9 wrote:

How do I disconnect someone’s Apple ID from a Apple watch

You get that person information to remove the activation lock.

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.