Heat activated patch. Can use a heat press (works best) or an iron with heavy pressure.
Heat iron to highest setting without steam option or heat press to 325° Cover patch with parchment paper and press for 25-30 seconds with heavy, even pressure. Let cool and check to make sure all edges adhered properly. Then press again for 15 seconds.
Wait to wash item for at least 48 hours to allow the glue to set in and completely harden.