If you deleted iCloud calendars or events from Mac
If you accidentally deleted iCloud calendars or events, you can use iCloud.com to restore them, together with your reminders, from an earlier version that was automatically archived in iCloud. When you restore an earlier version, your current version is first archived in iCloud so you can change your mind and go back to it.
Note: If you have shared calendars or shared reminder lists, all sharing information is removed when you restore calendars and reminders. You have to share your calendars and reminder lists again, and ask other people to re-invite you to share their calendars and reminder lists.
For instructions, see Restore contacts, calendars and more in Settings on iCloud.com.