If you want to configure your mouse options, press the “back” button on your device once mDosbox has started, to access the General settings. Then press “Gestures” and tick all the mouse tap gestures you’d like to use to control the right mouse button. You can chose either one or all of them: double tap, two point (2nd finger) tap, and long press. Confirm your choice, and everything should work fine.
Remember to save your changes before you exit the game (hit “back” button once again, tap “Save”)!