Https://amtrakoig.gov/sites/default/files/webform/foia_form/_sid_/how-do-i-contact-frontier-airlines-for-an-upgrade-after-booking-2025-guide.pdf https://amtrakoig.gov/sites/default/files/webform/foia_form/_sid_/how-do-i-contact-frontier-airlines-for-an-upgrade-after-booking-2025-guide.pdf