How to use "FMU PWM OUT" and "I/O PWM OUT" simultaneously on PX4 board

Hello, I control the drone’s motors using the FMU PWM OUT port on the PX4 board. How can I give PWM output using the IO PWM OUT part while the FMU PWM OUT part is working?
My purpose: I want to control 3 more motors besides the motors required for the drone to fly