Pour distilled water into the steam iron and set it to the wool setting.
Place the wool banner with the wrong side up on an ironing board.
Set the iron over the crease on the wrong side of the fabric. Leave the iron on the banner for one to two seconds and then lift up. Avoid running the iron back and forth over the wool fabric. Repeat the process on the next section of the banner. Continue setting the iron on top of the fabric and lifting it up until you have ironed the creases from the entire banner.
Turn the wool banner over and inspect the creases. If they remain, place a clean cloth over the top of the creases with the banner fabric right-side up. Repeat pressing the creases by setting the iron on top of the cloth and removing it after two seconds. The cloth protects the wool fabric from the heat of the iron. Continue the procedure until all creases disappear.
Lay the wool banner flat to keep any creases from reforming.