MP Joystick setup

Hi
I have setup gimbal configulation on cube with pwm on aux output and control it via joystick.
My joystick have only 2 axis which were bond to pitch and yaw control. I have set the buttons to control zoom axis by command “DO_SET_SERVO” which only send exact set pwm value. That made the camera just max zoom-in and out.
Is it possible to send the value by step? something likes 1 click for 10 pwm
And what dose this function do for joystick ? Button_axis0 and