To replace your original preset file, you can run the latest installer for your iZotope plug-in. This will replace any lost or outdated files but is designed to leave all of your other plug-in settings and files intact.
If you've overwritten a preset, you may need to rename, move, or delete the modified preset before proceeding. The preset will be stored on your hard drive as an XML file. After locating the modified preset's XML file, please rename or delete the file, or move it to a new location, to make room for a new copy of the original preset.
The default directory for iZotope presets are:
Documents > iZotope > [Product Name] > Presets