Bottle drop autonomous

Im trying to perform a bottle drop in a simple mission with Qgroundcontrol. I have my RC channel 9 set to aux1 triggering a servo that performs well using a switch. However when planning the mission waypoint how can I trigger the servo. Ive tried MNT_MODE_IN set to 3. in the waypoint i can show all values then set the SERVO number and PWM. But how do i link the servo number to AUX 1?