Open the Garageband software and select "File" from the top menu. Click "Open" and select a previously recorded audio project.
Highlight and select the track you wish to add effects to. Click the "i" icon, which is located on the bottom left side of the window.
Click to expand the "Details" section in the "Track Window." Scroll down and select the "Effects" option from the list. Scroll through the list of options and select the "Pop up" menu, which is located between "Echo" and "Reverb."
Scroll down through the list of effects and select "Audio Unit Effects" or "VST," depending on the type of plugin.
Select the voxReducer plugin from the list of options.