Hi @Dave Filson ,
Welcome to our forum!
As i know, when the meeting is saved as .ics file, only the organizer can update the meeting.
Trying to see if there is a way to set up or add Co-Organizer to outlook meeting invite saved as ICS file and invites has already been sent out..
As i know, the Co-Organizer feature is available in Microsoft Teams but not in Outlook. Only the meeting organizer and attendees are displayed in Outlook. In Microsoft teams, meeting organizer can set up or add a Co-Organizer. It's suggested that you could open Teams and do it. More information: Add co-organizers to a meeting in Microsoft Teams.
Hope to help you!
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