Call Southwest and ask them to add it for you. Generally, DIY adding of a TT number to your RR account after-the-fact will *not* add the TT number to existing reservations (and consequently you won't get TSA PRE on existing reservations).
While you had stomach flu symptoms, your doctor most likely prescribed a diet that consisted of bland foods and increased liquids. The BRAT diet is a common acronym used to treat an upset stomach and the stomach flu, according to FamilyDoctor.org. BRAT stands for bananas, rice, applesauce and toast.
The University of Maryland Medical Center recommends eating a high fiber diet to reduce stomach inflammation. Foods high in this nutrient include fruits, vegetables, dry beans and whole-grains. Some high fiber foods may give you gas, so avoid foods that create this problem.