This video covers how to synchronize your external calendar via iCal.

OneDesk allows you to synchronize your calendars via iCal with a link that is generated on individual users. You can access this link by going to the user panel right here and view the details on a specific user. So we’ll view the details on Chris by clicking three dots and click on ‘View details’.
Now scroll down and go under company permissions where you’ll find ‘publish my items to the external calendar’. when we check that it’ll come up with a link that you can use to copy/paste into your external calendar. That calendar can be either Google calendar, the Outlook calendar or the Apple calendar.Just copy this link on those calendars and your calendar will now be synchronized with the information from OneDesk.