If a purchased product is not working as described, the first thing you should do is head to the product page, above the images you should see the FAQ and Documentation tabs. Make sure to thoroughly read anything on these two tabs since in many cases common problems are explained here.
If you can't find an answer to your questions on the FAQ or Documentation tab you can try and contact the author via the product page. Here's a support document about how to contact Creators.
Please allow a few days for the author to get back to you. It is the vendor's responsibility to support their product. If you have reached out for support and haven't gotten a response from the author, you can contact the Blender Market team via [email protected]. If necessary, we will contact the vendor to resolve the problem.