I meant do NOT put heavy weights on your pad..my apologies it was a typo, however I guess you could put a weight on the back of the pad and see if it pushes the indents back out or try the washing method like Brundage said. If neither works, then I guess you'll have to purchase a new one.
One time I bought a brand new close up pad for about $30.00, went to a gig that night, used flash paper and it didn't go out before it went right down on my pad and singed a huge black spot right in the middle. Ouch...I was not happy.