Add an item to a list when not in list

[Martha]

When an item is not in the list, I want to add it to the
list table and to a field in the form table.

 

[Allen Browne]

Assuming that the value you want to add is the value that was typed in (i.e.
the bound column of the combo is not zero width), see:
NotInList: Adding values to lookup tables
at:
http://allenbrowne.com/ser-27.html