I'll state a few assumptions, then try to make a guess.
I think that you're a student who has been asked to submit your assignment via file upload, but are unable to either because 1) you are working in OneNote for Windows 10 and cannot find the file or 2) you are working in OneNote 2016 and are not allowed to upload the file to the assignment.
In either case, you could try printing to PDF and submitting the assignment that way. 1) OneNote for Windows 10 does not have a local file to upload and 2) it is possible that your instructor has allowed only certain file types to be uploaded for the assignment.
I hope that helps a bit.
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