If you are adding lots of sessions, take a step back and look at the event structure. Do the tabs make sense? Is it as clear and simple for your attendees (and yourself) as it can be? You can reorganize it by moving around tabs and sessions.
rename using the gear button
move under a different subgroup using the gear button
add new tabs using the Add new group button
rearrange the tabs by using the Change order button and drag & drop
select (a) session(s) you want to move
select either edit (pencil) or Bulk action > Edit
choose a new sub- or parent group using the select parent group menu.
View the new tab structure using the Preview button.
Create your event structure: http://support.networktables.com/en/articles/1200427-create-your-time-slots-event-structure-tabs
How to use Preview: http://support.networktables.com/en/articles/4950456-how-to-preview-your-event