This mod works with the 40th Anniversary Edition MSFS Grumman Goose G-21A.
Simple - drop file in community folder and a autopilot is enabled. Control the autopilot with keyboard bindings or other mods that allow autopilot control.
The autopilot panel pictured is from the paid version of the PMS50 GTN750 add on. You don't need it, autopilot can be controlled with keyboard commands or control bindings, it just makes it easier to see what the autopilot is doing.