Are you talking about being able to add items to combo boxes? Like in the List Items Edit Form

Yes. But, if it is not possible I will have to do with list Box

With a List Box, you can't type a new value directly into the list, you have to use the list items edit form which you get to from either the little icon that pops up when the field has focus, or through some other action like a double-click event.

If you are trying to just use the little icon that pops up to access the form, that is quirky because, once you've clicked into the list box, that disappears. It will only re-appear if the list loses focus and then gains focus again. Such as by tabbing to another field and then tabbing back, but then as soon as you select a new option, it disappears again.

However, once you've gained access to the edit form, it should work the same as the video linked above. List boxes and Combo boxes don't typically add records themselves but merely reflect records that exist either in the control itself, such as a value-list type, or via a table or field list. The edit form is what actually adds/edits/deletes records.

Thanks Mr. Blackwell.  But can this be done at all on a combo box?

On Not In List: Relational Combo (Extended Cut)
Also covered in Access Developer 35