Hello again, Assuming it is the Ryanair flight arriving 1825.
Assuming only carry on luggage - no waiting for suitcases
Best bet is to take taxi to Girona railway station.
Catch the 1917 train to Barcelona Sants arr 2031
Go up to concourse and purchase ticket to Tortosa (from media distancia counter)
Back down to catch 2103 train to Tortosa arr 2316 (or get off at Aldea a bit earlier)
There is also a direct bus Girona airport to Barcelona north bus station (Sagales is the bus co)
However, it requires a journey on the Barcelona Metro from the bus station to Sants
Hope that is useful