Have you entered your W-2 and verified your military rank when prompted within the TurboTax Online Product (Free Edition, Deluxe, Premium)? Your discount should be applied when you are ready to file.
Enlisted (E-1 through E-9) active duty and reserve personnel are eligible for the Military Discount. Commissioned officers, warrant officers, veterans, retirees and National Guard do not qualify for free TurboTax Online discount at this time.