Some folks have just left them out and they flattened and straightened on their own after time.
Others have used hot tap water, not boiling, to dip them in and then pin or tape them to a stiff object like a piece of cardboard or piece of wood to straighten them out.
I would go with the first method, leave them sitting out for a week or so and see if it works itself out. Then if it doesn't, try the second method.