Check that the patch and fabric are iron-safe
Preheat the iron to the setting recommended for the fabric
Turn off steam
Place the garment on a flat, heat-safe surface
Position the patch where you want it
Cover the patch with a thin cloth or pressing cloth
Press the iron firmly onto the patch for the recommended time
Apply even pressure without moving the iron around
Flip the garment over if needed and press the back side
Let the patch cool completely
Check that the edges are fully attached
Repeat pressing if any part is loose
Wash the garment carefully after the patch has fully set