I'm unhappy with my initial seat assignment on my Turkish Airlines flight, particularly because it lacks my needs. How can I change my seat after completing check-in?

To change your seat assignment, log in to your Turkish Airlines account and access the online check-in system within the specified time frame for your fare package. From there, you can select a different seat that better suits your needs and preferences.
Turkish Airlines offers online and mobile check-in for domestic and international flights.
Your fare package determines whether you can change your seat assignment, for instance:
For EcoFly and ExtraFly passengers, you can choose and change seats for free 24–90 minutes before your flight. This includes standard and paid seats with emergency exit or extra legroom.
PrimeFly passengers can choose free standard seats and pay for emergency exit or extra legroom within a 24-hour to 90-minute window.
Business Class passengers enjoy free seat selection during online check-in. You can replace standard seats once in a 6-hour to 90-minute flight.
However, keep in mind that once your boarding pass is printed, paid and free seat selection are unavailable.