To add TSA PreCheck® to your Delta Airlines profile, start by logging into your Delta account on their website. Navigate to the "My Profile" section, then select "Secure Flight Passenger Data." Here, you'll find an option to add your Known Traveler Number (KTN), which is provided when you enroll in TSA PreCheck®. Enter your KTN, and save your changes. Once added, your TSA PreCheck® status should be reflected on your boarding passes, making your airport experience smoother with expedited security screening.