Do two separate (at first) lines of experimentation. Get the arduino to control the servo motors according to an input signal. Look at the built-in-to-the-IDE example found at the IDE's File menu at Examples>Servo>Knob for a starting point. Then read up on the MQ6. Fancy-up the MQ6's output, and feed it into the servo as per the Knob sketch. After you get it working at the basic level, you can start making it better.