is there a trick to get iron burn off carpet?

Most carpet is nylon or polyester, and an iron doesn't stain those, it melts the tips. So there's nothing to clean out. If it's only the very top that went hard and shiny, snip the melted ends off with small sharp scissors, a little at a time, and brush the pile around it. Once trimmed it's usually hard to spot. If it melted down near the backing, the proper fix is a patch: cut a piece from inside a closet and swap it in with carpet tape.