Put an envelope with your address in the upper left hand corner and a stamp in the upper right hand corner in with whatever you are mailing back. That way the company can send you whatever you need and not have to pay for postage or an envelope
Put an envelope with your address on it, like youre gonna mail YOURSELF a letter, leave the address out of the top left corner, put a stamp on it,fold it in half and stick it into another envelope with their address in it unless they provided one to you and stick it in the mail. It's so they don't have to pay for postage.