How do I move OneNote files to OneDrive?

I've been trying to get my wife's OneDrive to backup her Documents to OneDrive. It won't, because it says there's a .one file in her Documents folder structure. (I've found it, but I'm not sure how to move it from her PC to OneDrive. All of my OneNote notebooks are in my OneDrive, but when I went to look where it saves those .one files, I couldn't find them. So, how do I move those .one files for my wife, to OneDrive.