PCA9685: how "unset" PWM signal?
You could try changing the corresponding pin from output to input.
To be sure not to disturb other comfigurations you could do direct port manipulation.

void servo_off() {
  DDRD &amp;= ~(1&lt;&lt;PD5);
}

void servo_on() {
  DDRD |= (1&lt;&lt;PD5);
}


This assumes you use pin PD5 for the pwm signal. Adjust the "D" in DDRD and PD5 so it matches the port in use as well as the pin number.

Of course, you need some additional user input like a button to trigger calls to those functions.