I bought a Apple Watch and it’s still linked to the previous owner Apple ID what do I do to unlock that

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 either ask the previous owner to unlock it, or you return it to the seller and get your money back. There is no way around Activation Lock.