At the FS Sound Studio Main window, select theFile: Open Sound.cfg by Aircraft menu pick. You'll see a dialog like this:
The installed Aircraft are presented in the left hand list. Selecting an Aircraft by clicking with the mouse results in a list of Panels and Sounds displayed for the Aircraft. At the top, you can see the current mode, and the directory in which FS Sound Studio is searching for valid Aircraft. This directory is relative to the one we specified in Step 1, and an example of why Step 1 is so important. If you don't see any Aircraft in this dialog, you probably need to revisit Step 1.
To help us determine which Panel/Sound combination is which, FS Sound Studio also displays the Title and UI Variation for the plane. (This is extracted from the aircraft.cfg file). You'll see the UI Variation in FS2002 when you're selecting Aircraft to fly in FS2002. Note that CFS3 does not support UI Variations for its aircraft.
Note that there are multiple Panels listed with the names Panel and Sound. In reality, they are all the same Panel, but differ slightly in things like ATC ID and external appearance. Sharing Panels and Sounds is a feature of Flight Simulator, but be aware that editing one will result in all of these Aircraft seeing the edits. Note that CFS3 does not share Panels or Sounds.
We'd like to edit the default C172 Panel, not the IFR Panel, so select C172on the left, and Panel on the right. Note that the changes we will make will effect all of the C172 Aircraft that share the same sound configuration named Sound of which there are 4. Click OK.