Only accept new data in libreoffice base

I’m working on a database using libreoffice base, im not going to be the one using it, so i have to limit the data, so the user will not be able to mess with the tables, i have this form where i can add the brand of a car, but i want to limit what the user cant input in the combo box based on what already is on the table of the brands, that is linked to the combo box, how can i do it

A Combo box will accept just about anything the user types whereas a Listboxe will limit the choices to a pre determined list of choices. Look at this tutorial.

Combo vs List Box