There isn't a way to delete all of your Gospel Library highlights and notes at once – you'll need to remove them one by one.
However, there is a view that shows all of your notes and highlights, which will be easier than trying to find them in content chapters:
1. Go to Home.
2. Scroll to the Study Tools card.
3. Tap Annotations.
From there, you can delete each one, using the three-dots menu (Android or iOS), or swipe to delete (iOS only).
Samuel Bradshaw • If you desire to serve God, you are called to the work.