When you duplicate a meeting, the same agenda will be copied as in the meeting you duplicated. However, you may need to be able to create an agenda from scratch or copy it from another meeting.
You can read about how to duplicate a meeting in the Meeting Duplication article.
In the duplicated meeting, click on the three-dot button and select one of the two options: Replace agenda or Clear agenda.
The Replace or Clear Agenda options are only available if the meeting and agenda have not been published. If the meeting or agenda has already been published - unpublish it and the options to replace or clear the agenda will become available.
Replacing an agenda will allow you to select the meeting from which you want to copy the agenda (similar to duplicating an agenda, which you can read about in the Agenda Duplication article).
Clearing the agenda will roll back the agenda to a default state, allowing you to create it from scratch.