Auto Complete and new value

in a form I have a text field that uses Auto Complete by taking the names of the cities from a View that groups the names with GROUP BY eliminating duplication.
It works great in finding the names of cities listed and saves correctly chosen values in the record
But if it doesn’t find any correspondence I would need to be able to type a new city and save it in the record
But if I type a new city it doesn’t remain it in the field and therefore it doesn’t save it
How can this be done?