Help to recover accidently deleted calendar data
This question is related more to Outlook than Android. Android syncs with google calendar and even if that case, deleted calendar events cannot be recovered (Google Support -
Can I recover a deleted Calendar event?  You can try to:


Go to your deleted folder in Outlook (yes I mean deleted mail) and check if deleted events are there. After deleting they go to this place.
Check if you have any Outlook backups
Check if you have any android backups, maybe you use Titanium Backup or similar software?


Other than that I can't think of any other way of restoring your calendar events