This would require a new settings option.
In the mean time if you want to change this across all attendance activities for all users you can edit \mod\attendance\lang\en\attendance.php
and the item 'strftimedmyw' which is set to '%d.%m.%y (%a)'
So you could change it to '%m.%d.%y (%a)' or '%Y.%m.%d (%a)'.
The change will be seen once the Moodle cache has cleared.
University of Nottingham