What are you seeing when you open Touchdown?
There are generally three ways to enter settings from Touchdown- the first is to hit the device menu key, and click the abacus icon.
If your device does not have a hard menu key, Touchdown should generate a soft menu key (for the LG G3, at the Touchdown Home screen, long press the icon below just to the right of your device home button.) If you are using a device on Android 3.x or above, you may want to uninstall Touchdown for Smartphones and install Touchdown HD, which includes the button, this can be found in Google Play.
Finally, if Touchdown opens directly to the inbox, just tap back (Or long press back and click on the Touchdown icon) to get to the main screen.