Question: can i add ktn to existing reservation delta?
Answer: Yes, assuming they issue you the Known Traveler Number (KTN) before you fly, you can add it to your reservation. As long as it's at least 72 hours (3 days) before the time of your flight, you can add the KTN to your reservation via Delta's website. After that, you'll need to call or visit an agent at the check-in desk.