Do you want to delete everything in the calendar? It is a little unclear if you want to remove and re-import or if you are trying to just remove duplicates. If you want to remove everything and re-import you can do it from the commandline with:
Code:
su - zimbra
zmmailbox -z -m account@domain.com ef /Calendar
.
the "ef" will empty folder, which you cannot do to the Calendar under the web client.
If you have the .ics file stored on the mailbox server, you can re-import it from the zmmailbox command with the PutRestUrl command
Code:
zmmailbox -z -m account@domain.com pru /Calendar /tmp/calendar.ics