Apple Watch pairing

You will have to get it unpaired to the previous account. Sounds like you purchased a second hand device. Contact the previous owner to have them remove the Activation Lock. Otherwise, you will not be able to pair it and use it. It will be useless to you at that point.

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 put it down to experience.