I'd recommend visiting Holden and buying a few spare white clips, as you may break one or two during installation. They are about 50c each, so half a dozen floating around your toolbox doesn't break the bank.
1 Firstly you need to remove the lumbar support dial (held by a circlip).
2 Once the dial is removed, start removing the rear panel from the BOTTOM. The top has guides, and if you snap those, you're stuffed.
3 The bottom panel is held by two white plastic clips, roughly 1/3 of the way in on both sides. Just yank them, let them snap, and replace them with the ones you bought from Holden earlier
You'll be able to figure the rest out. Just a note, it can be a pain getting the bottom two clips to line back up when you're re-fitting the panel. This is where a few extra clips can come in handy!