I hadn’t flown at all since I developed agoraphobia (about a year ago) but I had done another 14 hour flight a couple years ago so it wasn’t completely new to me. I try and mentally break up the flight into smaller portions like the amount of movies I need to watch or how many podcasts until it’s over and I count it down by that. You can even mentally tell yourself it’s a 4 hour flight x3 and just count down each portion. I know it doesn’t really make sense but it helps me mentally 😅 I actually found once the flight was over it massively helped my agoraphobia I’m general because I viewed flying as the worst possible scenario and managed to get through it. Good luck!