How do i get rid of purple stain i got after getting a temporary crown?

Answer 1

If by a "crown " you meant the thingy with jewels on your head, then it must be a really cheap tin material that reacted chemically with sweat of your borw.
Try rubbing alcohol.

If you meant a dental crown, then try baking soda

Answer 2

if the stain is on fabric hate to tell you you are out of luck---