PX4 Issue with Landing Gear Setup

I’m requesting help! Drone DJI S1000, Taranis X9D +, FrSky 9R & R9M. Replacing DJI N3 FC with a PX4. Having issues with Retractable Landing Gear wiring and configuring, “DIY”. Cannot locate detail instructions on how too. Please Help! I’m a “New Bee” at Drone RC builds.