"user1","user2","user3","user4","user5","user6" | Export-Mailbox -SubjectKeyWords "Confidential" -DeleteContent -IncludeFolders "\Calendar" -Confirm:$false
the -IncludeFolders switch means that it will only process the Calendar folder in the root of the mailbox
create an appointment in your mailbox and run it against yours
Export-Mailbox yourmailbox -SubjectKeyWords "Confidential" -DeleteContent -IncludeFolders "\Calendar" -Confirm:$false