If you forget to apply a patch on week 1 of your cycle following your patch-free week, apply it as soon as you remember. You must use another method of birth control for at least 1 week. The day that you apply the patch is now considered day 1 of your new cycle.
If you forget to change your patch on week 2 or 3, you can apply a new patch right away if you are 1-2 days late. The next patch should be changed on your regular patch change day. It is best to use backup contraception for 7 days thereafter.