To Delete a Button Assignment

Select Workspace > Button Assignments.
The Button Assignments dialog opens. The title bar identifies the open button menu.
Do one of the following:

Select a button assignment from the list box.

or
In the Buttons group box, turn on the Ctrl, Alt, and/or Shift check boxes and select the desired logical button from the list box.
Press the <Delete> key.
To save the changes in the open button menu, select File > Save or File > Save As in the dialog.
If you select Save, the open button menu is overwritten. If you select Save As, the Save Button Menu As dialog opens for creating a button menu with a different name or location.
In the Button Assignments dialog, click OK.