Bind a key on your Controller or Keyboard to Autopilot On and Off.

Turn On the Autopilot and the DA40 TDI will fly wings level and Altitude Hold. Turn Autopilot Off and fly again by hand.

You need the Premium Deluxe version to have this aircraft.

Installation: Unzip the Download into the Community Folder.

P.S.: The Autopilot can do much more, if you have all the keybindings or a controller for it. Just experiment.
I found it even does GPS NAV Mode if the Route is programmed in the GNS530 directly.