Here's a step-by-step refresher:
1) Create a software instrument track.
2) Click and hold the I/O button on the channel strip.
3) In the drop-down panel scroll down to "AU Instruments>Toontrack>EzDrummer."
If for some reason you can't do this you should check in HD>Library>Audio>Plugins>Components to make sure that your EZdrummer.component file is there.