Preheat your iron: Set your iron to the hottest setting that's appropriate for the fabric you'll be applying the patch to. Allow it to fully heat up. Make sure that the fabric is not made of nylon, vinyl, or leather, as these materials cannot be ironed on.
Prepare the patch and fabric: Place the patch on the fabric where you want it to be attached. Make sure it's positioned correctly and straight. Cover the patch with a piece of pressing cloth, such as a clean handkerchief or scrap of cotton fabric.
Apply heat: Place the hot iron on top of the pressing cloth and apply pressure for about 20-30 seconds. Move the iron in a circular motion to ensure that the patch adheres evenly. Repeat the process until you've covered the entire patch.
Check the bond: After a few minutes, gently try to peel the corner of the patch to see if it's securely attached. If not, reapply heat and pressure as necessary.
Cool and enjoy: Once the patch has cooled, you can enjoy your newly decorated item!