Ok, then for the DR400 it's "merely" about assigning this control to the starter button. But it will need to be different for instance with the PA28 or C172 that are started with the key.
There's no equivalent to the magic shortcut CTRL+E in FS that will start any engine whatever the aircraft.
Agreed, it should be a "merely", but I can't work it out and Larry Lynx Steve has found it a bit confusing too. If you are able to lend a hand