Position 2, theres the main fire button, the secondary fire button, and then you may have a 3rd fire button. I have 3 trigger buttons on my Joystick, 1 set to main, 1 set to secondary, and one set to fire both first and secondary. Press the button to fire first and secondary in position 2. Lemme look up the default key command real quick.
the default keyboard key is key "B". press B in position 2 and it will fire the MG.