Using older versions of Outlook for Mac in business environments
Unfortunately, the server update won't fix existing meetings automatically. However, users MAY be able to fix it themselves if they find the original meeting invitation (could be in Deleted Items) and re-accept the meeting(s) with the "UTC" time zones. (Let us know if that works.)
If that doesn't work, they will have to ask the organizer to re-send the invitation. (Organizer just has to open the meeting on his/her calendar and click "Send Update." Make sure to "Edit Series" if it is a recurring meeting.)