"Set servo" mission waypoint help

I can’t find any docs/info on how this works. I’m hoping to set a pwm output from the v5 and v5+ to control gear on a plane. Since I can’t get anything to work with the “gear” channel (MAIN6), I hope to get it working with this “set servo” in mission mode.
… 1.) How do I know which servo number to pick? I can only seem to get manual servo activation from aux1-aux3 (not counting mains - and main6 is dead). So does servo “1” = aux1?.
… 2.) will this work if it is included in a landing pattern, so that a failsafe - return to mission land will include it? I need to assure my gear extends on a failsafe landing.
Ps… This is a “standard plane” config. No mods.