Change the Organizer from Event Details
To move an event from one organizer to another, open the event in your admin console and select the organizer from the Event Details tab.
Select which organizer should be associated with the event on the Organizer Name dropdown.
If the organizer does not appear in the dropdown, you need to add or change the role of one of the organizer admins to "admin" in Settings > Manage Team and have them move the event to the proper organization.
Note: If an event has been published, you won't be able to move them to another organizer. You can unpublish the event first, then move it.