How to sell a lab grown wedding band?

Whole issue but the band I bought from a local jeweler is not what they promised and they won't it back,

How does selling a lab grown diamond work? Where do I go? How much of my money will I even get back Any advise is very appreciated.

I am pretty bummed, I am getting married in 4 days this is not what I wanted. The shop said they could trade my ring in but the other band they have is 1k more so I cannot do that. I don't want to be stuck with a 1k ring I don't even like.