Assign tablet stylus buttons

[Tadpole]

GIMP Version: 2.10.30
Operating System: Mac OS
OS Version: Mojave
GIMP Experience: New User

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I am trying to find a way to assign a tablet stylus button to 'edit.undo' the last action while using the pen.

Currently the stylus tip does the pointing and pen strokes. One stylus button acts like a Right Click mouse button and displays a context menu. The other stylus button changes to the 'Move' command. I would like this other button to 'edit.undo'.

I have investigated the Input Devices and Input Controllers settings but so far have not been able to make the change I am after.

Any ideas will be welcomed

Please note that am using an old Wacom GD-0912 tablet made usable by TabletMagic. Gimp does not display recognition of the tablet but it is working fine. Pen pressure / erase when the stylus is up ended etc etc)