If you have deleted old events in bulk from your calendar by accident that you wanted to keep, you do have the ability to restore those events to your calendar. There are three ways you can restore deleted events in your calendar: using a file that was created when you deleted items from your calendar, using your calendar automatic backups, and restoring a single event you deleted.
Restoring your calendar from a Saved Calendar Data file
When you delete events the deleted data is automatically stored as a backup in your Files application in your account. You can then download the calendar backup, return to your Calendar application, and import the deleted data back into your calendar.
To restore deleted events to your calendar you'll first need to navigate to your "Files" application. Follow the steps in the image below:
Once you have found the folder set in your account that has the "Calendar Saved Data" folder (generally this is the first folder set that was created in your account) you'll need to select the backup file that you want to import back into your calendar. Follow the steps in the image below:
Once you've downloaded the backup calendar file of your choice, you can then navigate back to your calendar and then import your backup into your calendar.
Restoring your calendar from a Backup Calendar file
Your account also regularly makes backups of your calendar. It holds up to 10 calendar backups at any time and it will delete older copies to make room for newer copies. You can go to the "Customize" screen of your calendar and in there you can choose and review which calendar backup you can restore your calendar to. See the image below:
Restoring a single event
If you only deleted a single event that you'd like to restore, you can go to the Calendar Edit History for the calendar of your choice. All you need to do is go to the Calendar Edit History, search for your deleted event, and then click on the "Restore" button next to it. Follow the steps in the image below:
Once you're in the Calendar Edit History make sure that you have the "Deleted" option selected for the "Only show these edit actions" option. This will make it easier to review only the events that have been deleted from your calendar. You can then click on the "Restore" button next to the event you want to restore to your calendar. See the image below: