Spare tire cover

Do it like the boat builders/cabinet makers do it...Steam it back into shape!!

Set up a sauna for it with a hot plate, tea kettle, some 2x4s and a shower curtain. Place the cover upside down on the 2x4s and place something like a phone book in the center of the high spot. When it straightens out, remove the tea kettle and cover and let the cover slowly cool and dry. It may take a try or two.