Customizing the Application > Customizing the Ribbon > To Move Buttons to or from the Overflow
  
To Move Buttons to or from the Overflow
1. To add a button to the overflow, on the ribbon, right-click the button and choose Move to Overflow from the shortcut menu. The button is moved. For the first button added, an overflow arrow appears next to the group name.
2. To move a button back to its group, in the overflow, right-click the command and choose Move to Group from the shortcut menu. The button appears in the ribbon group.