To add your Global Entry (Known Traveler Number / KTN) to an existing flight, you must access your reservation via the airline's website or mobile app and look for the "Edit Passenger Details" or "Add Travel Info" section. Once there, you will find a field specifically labeled for a "Known Traveler Number." Enter your 9-digit PASS ID (found on the back of your Global Entry card) and save the changes. In 2026, most major airlines also allow you to do this at the self-service kiosk during airport check-in or by asking a gate agent to update your profile. Crucially, adding the number ensures the TSA PreCheck indicator appears on your boarding pass, allowing you to use the expedited security lanes. If the indicator does not appear after you've added the number, it is usually because the name on your flight reservation does not match the name on your Global Entry account exactly, including middle names or suffixes, so be sure to verify that your profile information is consistent across both systems.