Smooth out the area that is creased with the palms of your hands. Get an idea of how large the creased area is and choose the size of the bag based on that.
Plug your iron into a working electrical socket. Find the lowest setting on your iron and preheat it to that setting.
Take the paper bag and lay it on the area that is creased. Flatten it with your hand as much as possible.
Place the iron on the paper bag and move it slowly over the creased areas. Do this two or three times, being careful not to allow the iron to remain in one place for too long.