To use a vuelo credit from an unflown flight, simply book your new flight on Flyfrontier.com. Once you reach the payment screen, select "Crédito con Frontier" and enter the confirmation code from the original booking (six characters, a combination of letters & numbers) to use the credit.
TENER EN CUENTA:
Credits are not redeemable for cash.
Los créditos pueden no cubrir la totalidad del valor de la compra. Any remaining balance due must be paid by the customer with a credit card.
Los créditos no son transferibles y solo se pueden canjear a nombre del pasajero a quien se le entregó.
The name on the new reservation using the credit must exactly match the name on the old reservation.