me21n custom tab

HI,

All I have created a custom tabin me21n with two fields in it vendor type and division with dropdown..

i division dropdown their are 5 names in it. the names shopuld change according to plant enter in  item level....

eg: if plant 1000 then in dropdown of division their should be abc,asd,qwe,

     if plant 2000 then in dropdown of division their should be xyz,abc.

     how can i get plant in header level..

i have used badi  header process.to pick plant from item to header in zzplant ekko field,

and used exit to export in subscreen but not working for me...

can any one please help with some solution...any exit or badi that can i use

Thanks in advance...