You can exchange a reservation for another reservation of the same type. You can also exchange a reservation from Azure Database for MySQL - Single Server with one for Azure Database for MySQL flexible server. It's also possible to refund a reservation, if you no longer need it. The Azure portal can be used to exchange or refund a reservation. For more information, see Self-service exchanges and refunds for Azure Reservations.
Reference: https://learn.microsoft.com/en-us/azure/mysql/flexible-server/concept-reserved-pricing
Hope this helps. Let us know if you have a different ask.
Thanks