TuneUp will allow you to "undo" or revert any changes you have saved to your music collection using the Clean features. Since Clean saves changes to both the media player library and the ID3 tags within the audio files, Undo will revert both. In order to "Undo", first go to the Undo sub-tab within the Clean tab:
Then you select tracks within the library of your media player that have already been "Cleaned" by TuneUp and drag them into the Undo sub-tab.
Once TuneUp has loaded and identified the list, you can "Undo" the entire list by clicking "Undo All", or Undo individual songs by clicking Undo next to each song. Clicking "Clear All" will clear the list from TuneUp.