I have received a [Known Traveler Number (KTN)][1] from the TSA but do not know how to "activate" this pre-check authorization with various airlines. 
 Is it possible to get this information into their systems when bookings for flights had preceded receipt of the KTN?


  [1]: http://blog.tsa.gov/2014/06/tsa-travel-tips-frequent-flyer-profile.html