Hi Ratana,
Follow these steps:
1) Go to transaction GSP_VPD
2) Select business transaction 0300,
3) Select accounting transaction variant
4) Copy variant 0000 to Z000
5) Add item category 04200 to Z000 variant
6) Go to transaction GSP_VZ3
7) Assign new Z000 variant to corresponding document types related with business transaction 0300.
Best regards!
PS: After this, you should also consider adjusting splitting rule with new transaction variant.