You already shuffled the names onto the bracket. You would like to restart. Erase the names and shuffle again.
Go to Brackets (Menu > Manage > Brackets/Round-Robins > Brackets)
1. Select the bracket
2. Click on Display More Options
3. Delete Opp. from bracket. (Delete Opponents from Bracket)
Do you really want to remove all opponents from bracket?
If you have a schedule, this does not remove the schedule, the Delete Schedules button does.
You can then go back to Fill Up Brackets and shuffle again.