Use product Thumbnail instead of Cover 1 [External Stores] [Gumroad]

I use Jinnxy to make my External Store products discoverable. However, for Gumroad listings, it uses the first image of the gallery instead of the thumbnail. Issue I have with that is that I need to have my 1:1 squared thumbnail as picture one which looks horrible on the Gumroad product-page for it to appear correctly on Jinxxy.