Both of my P3P's, one 3 weeks old the other 1 week.
From the Manual :

Camera Settings Dial

Turn the dial to adjust camera settings.
(Only functions when the remote controller is connected to a mobile device running the DJI
Pilot app. )

Turn the dial to adjust camera settings such as ISO, shutter speed, and aperture without letting go of the remote controller.

Move the dial to left or right to scroll through pictures and videos in playback mode.

Press down on the dial to toggle btween these settings.

Both of my RC Tx settings dials can not toggle between settings and will only adjust EV.

Press to toggle between ISO and Shutter Spoed is only available when you are in Manual Camera Settings mode...  In automatic mode, only EV adjustments are available.  Switch between manual and automatic by pressing the settings button in lower right of Pilot App.  Blue is Manual, Black is Automatic.  Swipe settings screen to left/right while in Manual mode to hide/show the settings screen.

TAZ Posted at 2015-7-10 09:04
Press to toggle between ISO and Shutter Spoed is only available when you are in Manual Camera Settin ...

Thank you TAZ. As I have not have attempted to change settings when in manual I will try that. Much appreciated.