How do I make my video the thumbnail for a gig

[shadowxsc]

I uploaded my gig video, all good. I searched for my gig on fiverr, just to see how it looks from the client perspective. It all looked good, a preview from my video and a nice little icon on the top-right to mark the fact that it was a video. But now I’m previewing my gig and I have my image as the thumbnail or cover, however you wanna call it, and not a preview from my video, as I had before.
My question is: how do I make my video the main/primary cover/thumbnail for my gig and not the image?

Thank you very much and have a nice day!