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The PBX will fill in the rest of the fields for you.
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Select Calendars
Once you have filled in the username, password and URL the list of calendars will automatically update.
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To view the calendar click the eye icon 
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You'll then see your events
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We can cross verify this with our Outlook calendar
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Edit Calendar
To edit the calendar's settings click the pencil icon
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The same settings will be presented from when you added the calendar
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To remove a calendar click the trash can icon