Hi,
Your Query is wrong. How could you modify table VBRK with Kna1? Both structures are different .
For your requirement Use
1. user exit 'RV60AFZZ'.
2. The logic must be used for debit note. so control via vbrk-fkart = 'Debit note type'.
3. Get the corresponding SO for invoice (if payer from SO) .
4. Gather information from VBPA table for payer.
5. Modify VBRK table for corresponding field (use transporting field).
Thanks & Regards,
SABARISH