I found this solution in the answer forum:
However, this is for an older version of Word. When I use the new Word 365 on Mac the info is in Preferences->User Information, and it seems to default to "Microsoft Office User". Ok, fine.
My problem is that I have a Word document with thousands of comments already inserted, and they all have my real name on them. I want to CHANGE all comments with my name to anonymous. Again, these comments are already in the document.
Can this be done?