Start by signing into your MileagePlus account on the United Airlines website in order to add TSA PreCheck to your reservation. Enter your Known Traveler Number (KTN) under Personal Information after navigating to the Profile section. If it's not there, add your KTN and save the modifications. How Do You Add TSA PreCheck to United Airlines change the Traveler Information area with your KTN for active reservations, go to the "Manage Reservations" tab, choose your booking, and update it. Other options include adding your KTN when checking in online or giving it to a United representative at the airport. Your boarding pass will display the benefits of TSA PreCheck if all requirements are satisfied. Verify that your KTN is accurate and related to your flight by checking.