Badges are signs of progress and honor among scouts, and most of them go on the uniform. Badges can be sewn on, but most use a "peel and stick" adhesive so they can just stick to the uniform. It's possible to iron some badges on, though this isn't commonly done. Check the patch itself first since some are not designed for ironing. The patch should have a glossy back.
Place the shirt on the ironing board. Place the patch on the appropriate spot on the shirt in accordance to scout rules.
Set the iron to a medium setting.
Place a thin pillow case over the patch. Press the iron to the patch using heavy pressure for about three minutes. Check a corner of the patch. If it's not stuck, try the iron method again.