Scheduling and managing events using Outlook.com calendar
Do you use outlook desktop? (It's easier if you do.)
if the events were over written, they are gone. If they were deleted - you can look in the deleted items folder in outlook desktop - in the Folder list view (Ctrl+6) - turn off the reading pane and sort by the icon.
If they aren't in the deleted items folder, they might be in the recovery folder linked at the top of the deleted folder.
It's easier using an Office addin called Email Recovery. It can recover mail that is in the recovery folder or in the purges folder. It creates a new folder for all of the recovered items, so you don't pollute your folders with old items. When done, deleted the folder then delete it from the deleted items.