Restore your calendars and events on iCloud.com
You can restore your calendars and events (along with your reminders and reminder lists) from an earlier version that was automatically archived in iCloud.
If you have shared calendars, all sharing information is removed when you restore them. You have to share your calendars again, and ask other people to reinvite you to share their calendars.
If you do not have shared calendars, go to the next step.
If you do have shared calendars, write down which ones you are sharing, who you invited to share each one, and whether each participant can view and edit or only view. Also note which calendars other people are sharing with you.
On iCloud.com, tap
in the toolbar, then tap Data Recovery.Tap Restore Calendars (or Restore Calendars and Reminders if you are not using upgraded reminders).
Available versions are listed by the date and time they were archived.
To the right of the version you want to restore, tap Restore.
There may be more versions than can be displayed. Scroll to see them all.
Note: Wait until iCloud finishes restoring your calendars before you change them. During the restore process, any changes you make are not saved.
If you had shared calendars, reshare them and ask other people to re-invite you to share their calendars and reminder lists.
The restored calendars and events appear on all your devices with Calendars turned on in iCloud settings.
If you change your mind, you can restore the calendars and events you were using. Simply follow the steps above to restore the most recent version available.