Press the Mode button, then turn and press Value Encoder 1 to switch between controlling the internal Haken Audio EaganMatrix sound engine and configuring the behavior of the External MIDI mode. The two modes will always run in parallel. Selecting a mode only decides which mode you want to access and configure.
A symbol in the upper left corner will indicate the currently selected mode at all times:
Pressing Value Encoder 4 while in Mode Selection screen opens the global settings of Osmose. They allow you to change the global tuning, calibrate pedals, display the firmware versions, change the screen brightness, etc.