If you are using iOS or MacOS , iCloud is preinstalled on this device. It stores user data securely. But if in your device if iCloud for Outlook not working then you can fix this issue within following steps:

On or off the iCloud contact & calendar.

Check whether iCloud Add-in is active or not.

              Go to File Menu > Click Ads-in option in the left side of Outlook window

              Check Ads-in active section list

              After that select Outlook Ads-in option

Set Outlook as default account

Logout the iClod after some time again, sign in and add it.

Update software if not updated.