You need to first enters in development mode from the touchscreen. To do this, goes to setting -> about machine, then just press on the screen about 5 times consecutively (just as how to get development mode in standard android).
Then there will be two more icons on the main screen. Go to Experiment -> Preference -> Reset all. This option will clear out the on screen settings including calibration values (also the wifi thingy). But not the EEPROM from the controller (so all the G and M gcode settings)