SERVO_FUNCTION definitions for a tail sitter

I do not know where to ask for help but here goes. I am building a ARKBIRD kit unfortunately it has no manual. The build is not a problem as I have built many planes and quads over many years. I have converted an Skywalker X5 to autonomous flight so I thought this project would be simple. I used a Pixhawk 2.4.8 flight controller and QGC as the interface. Here one defines SERVO1_FUNCTION = 77 etc. but now I am stuck. Where are the two ESCs connected and where are the elevon servos connected to the Pixhawk. All I have found in the documentation is SERVO5_FUNCTION = 75 an SERVO6_FUNCTION = 76 and a bit further SERVO7_FUNCTION = 73 and SERVO8_FUNCTION = 74. So I am totally confused.
Thanks in hopeful anticipation