Hi Naveen,
Already everyone told you to use FM CONVERSION_EXIT_ALPHA_INPUT/OUTPUT for getting values With / without preceding zeros. Let me add few things in that.
First fetch data for KNVV table loop that internal table use conversion routine FM
(CONVERSION_EXIT_ALPHA_OUTPUT) inside your LOOP.
populate new internal table probably you can say Temp table and use;
SELECT ... FROM BSID
FOR ALL ENTRIES T_TEMPIATB
WHERE BUPLA = T_TEMPIATB -KUNNR.
As your BUPLA is 4 CHAR long you should use KUNNR first to remove preceding zeros.
Hope this will help you.
Regards,
Nikhil