Need to bring fields in NWBC screen

Hi,

I need to show some of the fields which are existing in the data model in the NWBC screen. The problem is when I am wanting to show a field say KUNNR (customer) in one of the screens in vendor as per my client's requirement I am unable to find that field in the list of the fields which I can add.

The arrow pointing to the yellow highlighted section is the place where I want to add my KUNNR field.

See the area marked in blue I cannot find KUNNR to add at this level. Is there any way I can achieve this?

Thanks,
Subhronath