Typically OneNote won't let you easily view files behind the NoteBook without a little bit of work on your part, I haven't managed to find any guides that detail the steps you need to take.
First off, if you're doing this to a Class NoteBook you will need to be an Owner/Teacher of the class in question before you can do this. The second step is to find what I call the "Section Name" of the NoteBook, for example in my scenario the NoteBooks are called Section_Year* E.G: