confused on the repaint kit in IPAC's website

I'm quite interested in this, as I want to personally make myself a new livery. The thing is, I followed through with the instructions, but it shows me a blank preview. First, I test if the preview appeared, which just appeared blank (no preview of the aircraft; for more context, the base livery is china southern which i download from flight-sim.org). can somebody give me a clear explanation of the tutorial, as i do not know what i did wrong, or, better yet, i kinda need a video demonstration