someone talk me through getting an iron burn out of a carpet?

If it's only the tips that went brown, get small curved scissors and snip the scorched ends off, then rub the pile back together with your fingers. Most light iron burns disappear that way. If the fibres melted into a hard crust (common with nylon or polyester carpet), cut that crust away the same way. Burnt right down to the backing? Then the only real fix is a patch. Cut out a square, take a matching piece from inside a closet or under the sofa, and stick it in with carpet tape.