Updated for Version 7+
On the left navigation under EVENTS, click on PARADE. You will be taken to this page:
In the list of Groups, click on the Float name. A pop-up will appear that looks like this:
Select ASSIGNMENTS in the top right-hand of the screen. This will take you here:
Click the RESET FLOAT button above NO ASSIGNMENTS
This will clear all assignments presently on the float.
This CANNOT be undone