The unique service «Refund/Exchange ticket» gives an opportunity for a one-time free change of the date/time of departure or refund no later than 48 hours prior the flight departure. You can buy the service only during the initial booking flow process, you cannot do it later.
Please pay attention: if the date or time of flight is changed, the cost of the new ticket may be higher than the original. In this case, the difference in the cost must be paid by the customer, while if the cost of the new ticket is not higher than the original one, the customer does not have to pay an additional fee. But the difference in the fares will not be returned to the customer.