To Delete a Button Assignment

Select File > Settings > User > 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.
If you wish to save a button menu with a different name or location, click Save As Button Menu.

The Save Button Menu As dialog opens.
To save the changes in the open button menu, click Save.
The open button menu is overwritten and the Button Assignments Dialog closes.