It appears I may be wrong.... It must be region specific the other members in this thread can advise you better than I can because I'm on the wrong Coast and it doesn't work in my account. My apologies seems I'm jumping the gun all over the place today.
Hello from the South Shore! If you sign into your account and go to "plans & add ons" there is a spot there to enter a promo code, once you enter the promo code the data will automatically be added onto your account. Have patience though, the site is rather slow today