The normal way to undo is to press the Esc key one time for the last control
edited or a second time to undo all the changes to the record. When you
press Esc for an option group, it will change it back to the last selection
in the option group, but not back to a Null status (i.e. no selection). To
do that, you will need to use code to set the value of the option group to
Null. This could be done in the click event of a button. You could place a
button next to the option group and call it Clear Option Selection. The line
I gave previously would go in the VBA editor in the button's Click event.
Replace FrameName with the name of the frame around your option group.