Just insert it on a vocal track. The vocal track will serve as the modulator. If you don’t hear anything, that’s probably because there is no signal present at the modulator input, or the signal is very weak. If you have any meaningful signal in the track you should hear it modulating the noise generator and clicking on any of the keyboard’s buttons should introduce the modulated internal carrier sound. You can click the little question mark in the corner and the manual will pop up.