Go to Sign-up.
Select Sign-up from the site Tool Menu.
Select a meeting name to open its details, and then select the Copy link at the top.
Make desired changes, then select Publish New Meeting.
The Copy this meeting details page will appear. Change the settings as desired, then select Publish New Meeting.
Note: Some settings will not be available to edit. You cannot copy a multiple-slots meeting into a new single-slot meeting, for instance.