How to change PWM frequency for AUX Channels?

I want to run a brushed motor off one of my auxiliary ports on my pixhawk - but it doesn’t seem to like the Normal PWM frequency from the main channels. I read about being able to change the SERVO_BLH_OTYPE parameter to change the frequency but I’m not sure where to go from there, do I need to configure SERVO_BLH_MASK to enable this on a specific pin of my aux output?