PWM signal from the pixhawk

I would like to know where can I find the waveforms of the PWM signal produced by the pixhawk?

I think you have to use DSO for output waveforms.

Instead, is it possible to change the duty cycle of a PWM signal coming from pin 7 (RC7 / P7) of the pixhawk?
If so, in which file is the relative code and with what software can I edit it?

I have viewed it with an oscilloscope and I would like to change its duty cycle.

How would you like to change it and why?
You question can not be answered without more information.