[stumped]

try spray on carpet cleaner ? [ remove the kindle first]

the official amazon cover I have on my Fire HD10 tablet is like cheap blue material stretched over what's probably stiff cardboard. A complete rip off at £25 - frayed around the edges already and the tablet never leaves the room. the fraying is just from holding it/propping it up to stream video.

I just accept that the cover is naff but the tablet inside should be pristine, if ever I try to sell it. Prices for used Fire tablets are very low though because Amazon keep bringing out newer, cheaper models, and making huge price reductions on every prime day/ black Friday, or random throw-of-the-dice lets-have-another-sale day.
the old origami covers were made of a hard plastic which is much easier to clean, and harder to mark