1. Start in your vcita account. 
2. Go to Settings > Staff (just Settings for non-admins).
3. Click the ⋮ icon next to the staff member you want to sync the calendar to and click Edit Staff Settings. 
4. Switch to the My Schedule tab.
5. Click Disconnect next to your synced calendar.

6. You may now select one of the calendar options to sync a new calendar.

Further Reading:

• Sync Your Google Calendar to vcita
• Sync Your Outlook Calendar to vcita
• Sync Your iCloud Calendar with vcita
• Sync Your Yahoo Calendar to vcita
• Sync an 'Other' Type of Calendar to vcita