To use the VST, you need to authorize the app. iZotope will email you a registration code that you'll use to authorize. The email also contains a link to a download section. You need to download the iDrums app from the website as it contains the VST. Plus, while you're there be sure to download the acoustic drum kits. You don't need to download the other kits there as they were installed with the app store download.
It's a simple app tp use, but offers a lost of customization, i,e.: MIDI note assignment, import samples, etc.
One odd thing when using the VST plugin with EigenD: it's GUI does not automatically load. Maximize the GUI window and it will show up.
Randy