I don't have the program so I can't tell you how to set the HSI directly. I have been trying to research it and I think that you set it with the FMC. You will have to check with the manuals that you get with the program or some one that has it. Originalgrunge's post above should lead you in the right direction.
From everything that I've heard about PMDG 747, it's one of, if not the best, 747 simulation programs you can buy. The problem is that flying a 747 is very hard, even in a simulation. They try to make it as real as they can. When real pilots get to the First Officer(Co-Pilot) seat of a 747, they have been flying for over 10 years. It still takes them 2 months of 747 training. I simply meant that you need to learn the basics of IFR flying, IAP charts, autopilot operation, GPS and VOR navigation, on a easier to fly aircraft first. Then you can move up to the 747. You're in computers. In computer world, this is like someone trying to set up a server and write C++ programs when they don't even know what a CD-ROM is! Start with the Cessna 172 and work your way up. 🙂