According to the Delta flight refund policy, odds are that you purchased a non-refundable ticket, in some cases; the ticket dropping (cancel) charge will be deducted from the total price of your ticket. The entire surplus sum will be given in the form of eCredit that can be used at the hour of purchasing another flight ticket. A form of tickets, for instance, Basic Economy flight tickets, can't be canceled.
Those flight tickets that have not changed past takeoff will have no excess worth. Specific tickets, like Basic Economy, can't be changed after you have crossed your flight Cancellation duration. Due to any condition, your plan changes and you want to cancel the flight and make a reservation on a refundable ticket, you can request a refund based on delta flights cancel policy.