Are you asking how someone can export members from a Segment in Customer Insights Journeys? If so then it can't be done at the moment. There's several other methods of doing so though.
I'll link you a programmatic way of doing it here:
Amey Holden also has a few articles on how to access the list but again there's no real out of the box method to export it to Excel but with this you'll be able to understand how they're stored:
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