How do I fix incorrect thumbnail images?

[KingCurrency 0]

For some of my video files, the thumbnail is showing a picture of the artwork for the season instead of for the individual show. What I'm trying to say is it shows the same image (season 1 thumbnail) for every episode in the season instead of showing a frame of the actual episode for the thumbnail. What causes this and how do I fix it?

[Luke 42077]

Downloading the episode image may have failed. Try clicking onto the episode screen, then click the 3-dot menu -> Edit Images. Try manually downloading a new episode image.