Just to clarify what people are trying to tell you to do. You'll need to:
1. Purchase a DSiWare game on your O3DS. Also Steel Diver if you don't have OoT3D/Pokemon ORAS/Cubic Ninja/Freakyforms (if you do, you'll need an NEW NNID for this, it will be disposable).
2. Follow the guide, do a system...