For domestic and international flights departing from the United States, Delta Airlines no longer charges a fee from their passengers to change flights. If your new flight ticket is more expensive, then you will only be required to pay the fare difference. However, the fee waiver does not apply to basic economy tickets, which are non-refundable. In some circumstances, you may be able to change your flight (date, time, and/or destination) or request a refund in the form of an eCredit under Delta Airlines flight change policy.
https://airlinesinfos.online/flight-change-policy/