How can I remove spurious posters and backgrounds

I added a single episode of a 2020 TV documentary series and Plex matched it to a similarly named series from 1990, and added a poster and background. Seeing this was wrong, I fixed the match by using the reference number of the series from TheTVDB, which then matched correctly. However it did not correct the poster, thumbnail or background. There doesn’t seem to be any way to select the spurious images in edit and remove them. I can manually upload an image and select it as an additional image but I shouldn’t have to do this; the episode has been correctly matched (the synopsis is accurate), the inappropriate images should be deleted (or at the very least they should be manually deletable). Have I done something wrong? What’s the correct fix here?

Trumpy’s tips should get the right images, but removing the incorrect ones is not possible in the UI. There is a feature request to add the capability.