How do I have both custom show tv art and custom episode thumbnails?

I have a homemade tv show that I want to add to the Apple TV app on my Mac. I've imported the show, added all the metadata I want to, and I want to add thumbnails for each individual episode, as well as a different image for the show as a whole, just like every other show in the app. When I set the individual thumbnails, and it looks good, and then I add the show artwork, and it overrides the episode artwork. So I try it the other way around: add the show artwork, then the episode artwork. When I do *that*, the show artwork is replaced by episode 1's thumbnail. How do I have both custom show art and custom episode thumbnails? Big Sur 11.0.1