a new cover. sorry...scorch marks may fade a little with time and extensive treatment (peroxide- blotting, more peroxide more blotting) but to actually remove them? cut them out and apply a patch, or buy a new cover.
when i bought my newest cover i wanted it to last so i started ironing a piece of freezer paper right to the top of my ironing board...over the cover..i use it for fusables, sprays, what ever, when it gets (yukky) i peel off the paper and replace with a new piece. now my cover always looks new.