I bought this Apple Watch off market place I cannot pair it because it on another Apple ID??

You need to contact the previous owner and get them to follow these steps;

What to do before you sell, give away, or trade in your Apple Watch, or buy one from someone else – Apple Support

If you can't contact this person then take the watch back and get a refund from where you bought it.

The watch has an activation lock on it and can only be removed by the person that originally setup the watch,without the original apple id that set it up then the watch is of no use to you.