Depends on the plastic. Some plastics don't really take to superglue, pushing the dried glue hard will often make it fall off. Other plastics, well, super glue works by causing a chemical reaction between itself and the things it touches, causing the things to melt together (so to speak). In that case the plastic has been permanently damaged and all you can do is rub back and paint over it. Or some other remedy (depending on the type of surface).