Bastia Poretta Airport: Rent a car at the airport; Oletta is roughly a 40–50 minute drive, depending on the mountain approach and traffic. This is the actually useful option: there is no rail service to Oletta and public transport in this corner of Corsica is too infrequent to structure a holiday around. A taxi is possible but should be pre-booked and will be expensive.
Bastia ferry port / Bastia station: Pick up a rental car in Bastia and drive about 35–45 minutes to Oletta. Bastia is the rail terminus for northern Corsica, but the train does not continue toward Oletta. The limited Bastia–Saint-Florent bus is not a practical Oletta transfer: it runs only once or twice daily Monday–Saturday and not Sundays, then still leaves you outside the village.