It is very easy to customize your garments by ironing items on them. You just have to follow the following steps:
1. Heat with the iron the surfae on which you are going to place the patch for 20 seconds
2. Place the patch in the previous heated place
3. Use a piece of cloth or a rag over it as a protection and iron it for 30 second on the right and 30 seconds on the revers. 
4. Wait 30 seconds
5. Repeat the same action for the rigth and the revers
6. Keep in mind the most delicate arear and the edges of the patch so you should press the iron a little harder
7. Done. You have customized your garment and it's ready to be worn
8. Do not wash it before 8 hours. After then, it can be home washable at 30ºC