Go to Attendees and check the filters you can choose
Explanation of attendee email segments:
Before you can send an email, you need to decide to whom you want to send it. You can do it by selecting a segment.
Seated = all people seated in a session (including hosts)
Not Seated = all attendees that did not choose a seat yet
Need welcome email = all attendees, excluding session hosts, that did not receive the welcome email yet.
Need first reminder = all attendees that received the welcome email to choose sessions/request meetings but did not take action yet.
Table host = are all the hosts of the sessions (for 1on1s, roundtables and workshops)
If you click on "create segment" you can create your own segment with filters. Read this article.