External users directly can't be made as presenters without inviting them as Guests into the organization.
**Refer to documentation **plan-for-teams-live-events
For a guest to present in a live event, do the following tasks:
- Add the user as a guest to a team.
- Have the user accept the guest invitation and join the team.
- Schedule the live event and add the guest to your event group.
Hope this helps.
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