Within the left side navigation bar, select My Group. This will take you here:
Within the horizontal navigation bar, select Manage Float Assignments. This will take you here:
Within the Layout box, there will be a list of names under the No Assignment column.
Drag and drop the name of the desired member into their respective float position. Your page will now look like this:
Once you have assigned members to their desired positions, select the green button titled Save Float.
If you do not save your float progress, the names will not appear within the float assignments once you leave the page.