Using Classic Outlook on Windows for personal email, calendar, and contact management
Unfortunately I don't think you can undo this. Once the history is lost, it's lost.
The best you can do is make sure it doesn't happen again. Do all your calendar editing in the web version, not the desktop version. It has the capability to make edits of "this event and all subsequent events", which the desktop version does not.
I now keep my Outlook calendar as one of my home tabs in Chrome and do the rest of my Outlook work in the desktop version.