SO we have options for making our process make them NON-PRIVATE if you wish.
OR if you want to migrate it as private and then change it, this VB script will help.
Sumatra Development leads the field of migrating entire calendar servers to Exchange. We migrate Oracle Calendar Server, Oracle Beehive, and Zimbra to Microsoft Exchange keeping all meeting information intact. We are migrating calendars server-to-server between Exchange and Office 365 while keeping meetings live and doing incremental syncs. We just added Apple's PostgreSQL iCalendar server to Microsoft Exchange calendar migration.
Free license through 2017 if you qualify and contact us . First: you can always get help at the PowerShell prompt with: get-help Get-suDo...