PWM 0-13 channels are available on 2.54mm header pins numbered 1-14 accordingly. Servos can be controlled by setting the correct frequency (50hz is a common frequency) and duty cycle corresponding to the length of a pulse (usually between 1 and 2 milliseconds).
To try to control servo connect the servo to the Navio’s output channel number 1 and run the provided example. Do not forget to supply power to the servo rail.
If you haven't already done that, download Navio2 drivers and examples code here.
Move to the folder with the source code, compile and run the example
cd C++/Examples/Servo make sudo ./Servo
Move to the folder with the code and run the example
cd Python sudo python Servo.py
For further information see cource code. Note that
set_period function sets the period for PWM_OUTPUT channel depending on frequency value,which passed as a second parameter to the function.
To set the pulse range appropriate for your servo you can change the SERVO_MIN and SERVO_MAX values.