Controling a fan on Rock 3C

I’ve connected a small fan to the 1.25mm header on Rock 3C. How can I control it?
After doing some research, when I try this:
“echo 0 > /sys/class/pwm/pwmchip15/export”
I get this error:
“echo: write error: Device or resource busy”

In ‘Thermal governor’ from rsetup, I switched to every option there is, and nothing changed.

Can anyone help me please?

not sure if it help, but I’ve been using a fan with 3C using the step-wise setting in rsetup.

Been working fine, at 60C the fan turns on a fairly low PWM but that generally enough to keep the CPU from going over 65. I’m using a 25mm fan to move air in one end of my enclosure with vents at the other end.

I’m also trying to use a 25mm fan but no success so far. I also tried to set step-wise in rsetup, and the fan won’t spin even if the temperature goes above 60C. The fan is fine, it’s working when i connect it to a 5V source.
And still can’t figure it out how to controll it manually. Here’s what i tried earlier:
I removed the pwm-fan module to unlock pwmchip:

rmmod pwm-fan

then I did this:

echo 0 > /sys/class/pwm/pwmchip15/export
echo 40 > /sys/class/pwm/pwmchip15/pwm0/duty_cycle
echo 100 > /sys/class/pwm/pwmchip15/pwm0/period
echo normal > /sys/class/pwm/pwmchip15/pwm0/polarity
echo 1 > /sys/class/pwm/pwmchip15/pwm0/enable

the fan still won’t spin.