Is the discrete for antenna input already in the Harmony database? Go to Device mode for the TV and see if there is a command there for Antenna Input, and if it works properly.
If it is already in the database, go to your home page and select "more options" on the TV device. On the next page select "adjust inputs", then "I go directly to the input I want". Make sure the list of inputs matches what your TV actually has, then press Next.
Then for each input select "Use these infrared commands" and choose the command you found in Device mode.
If the discrete isn't in the Harmony database already(unlikely), but you can find the Pronto hex for the command on the net, you'll need to email the Pronto code to tech support and they'll add it to the database.