iCloud Calendar
Log in to iCloud.com in your browser.
Click on Calendar.
On the left side, find the calendar you want to access in Clockk.
Click on the wifi-on-its-side icon. You'll see a panel appear with sharing options.
Click the ”Copy link” link.

Paste the webcal://
link into the “ICS URL” field in Clockk.
Name your calendar after the email address associated with this calendar.