Just starting out. Need help with syncing calendars

Just starting out. Need help with syncing calendars

I am trying to set up our guys to have calendars on their iphones using activesync. First thing is setting up their calendars on zoho calendars. When I sync the Zoho calendar from CRM, it makes their CRM calendar a secondary calendar instead of their default calendar.

How do I make their zoho calendar their default calendar so that I can activesync it to phones?

Thanks!