I have on my storage somewhere a book on generic airliner systems. I think it is published by Jeppesen. It covers the typical system designs for electrical, hydraulics, pneumatics etc. Once you grasp the basic design philosophy learning a different type becomes a lot easier. Also search for a book by Jim Webb called “Fly the Wing”. Its a bit dated but it has valuable strategies for passing an typical FAA type rating as well as an exhaustive discussion of high speed aerodynamics and swept wing characteristics.
Good luck in the new gig. And very good on you for honestly posting about your difficulties on that first course.