You can rename any list on a schedule item. The name is the heading attendees see above that group of people, so it's worth matching the words your event actually uses.
To rename a list:
In the schedule item, click the ⋯ button in the list's header.
Choose Rename.
Type the new name. As you type, Yapp suggests names you've already used on other sessions in this schedule, so the same role is spelled the same way everywhere.
If another list on the same schedule item already uses that name, Yapp asks you to pick a different one.
Renaming a list changes this session only. Lists with the same name on your other sessions keep their names.
Related articles that might be helpful:
Start with the guide to lists on schedule items
See how you can reorder the lists on a schedule item