If you purchased your ticket with Armas Trasmediterránea before the transfer of the Alborán and Estrecho routes to Baleària, you can modify only one of the legs of your booking, either the outbound or the return.
You can also modify the pending leg even if you have already completed the other. If the change only affects the date or time of the journey, it will be made without penalty and maintaining the original price.
Related to