Why VTOL tiltrotor can not stop the rear motor?

hello guys:
I Use the VTOL tiltrotor,ater the plane trans to FW mode, the rear motor should be closed. But on my plane , it still
on. I test the pwm output ,USE pwm max -c 3 -p 1000 ,but the max pwm out is still 1400. Can anyone tell me how to stop the rear motor after my plane transed to FW mode?

The max PWM value cannot go lower than 1400 (by design). You need instead to set the motor to stop using the VTOL configuration parameters.

thanks,but can you tell me how to do to istead the setting?