OneDrive (and Office apps like Word, Excel, and PowerPoint) automatically keeps track of versions when a file is edited.
In OneDrive online:
Go to your campus OneDrive (visit myEOL and select OneDrive in the Office 365 section).
Locate your file, right-click, and select Version history.
Browse older versions, preview them, and click Restore if you find the one with the missing content.
In Word/Excel/PowerPoint desktop apps (when opened from OneDrive):
Go to File > Info > Version History.
Open the older versions side by side.
Restore or copy/paste content back into the current version.