How do I delete multiple (all) Marks?

You can display the marks in a list, select them all and delete them all. 

1. On iPhone: Tap the Mode  button  (far right of the Play Button) and selects Marks
   On iPad: Tap Songs (top Left) and select Marks on the selector at the top.
2. Tap Edit
3. Tap the Checked Circle to select all the Marks
4. Tap the Trash Can
   
   This deletes all the marks in that song. 

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If you play all your music from your device's music library and do not use folder or playlists, you can delete all the marks from many songs by deleting the songs from All Tunes. 
When you Play a song for the first time it is  added to the  All Tunes list. You will also see an Info Button on the Song in a list. Anytune is now remembering all the settings (Tempo, Pitch, marks, notes, lyrics,....) for that song. 

Deleting a song from "All Tunes" will delete all the saved settings and the song in Anytune. You will not delete the copy in your device's music library and can play the song again from directly from your music library of your device via the  Songs,  Playlists,  Artists and  Albums categories.

To delete a song. 

• Swipe Left on the Song in a list and Tap Delete
• Tap the Info Button and Tap the Delete Button
  
• From the Playback View, Tap the Song Title bar and Tap the Delete Button

When you import a song into Anytune directly through Open-In, Files Pickers, Email, WiFi it is the only copy, and deleting it from Anytune really deletes the file. 

Deleting a song from a Playlist will not delete it from "All Tunes" or from Anytune. It will be deleted from the playlist only.  

Deleting a song from "All Tunes" will delete all the saved settings and the song in Anytune. You will not delete the copy in your device's music library.