code in ZXVVFU04 for user exit EXIT_SAPLV60B_004

Hello,

We are trying to get the internal order field from a SD order to FI into the segment field when doing the SD billing.

We believe that the right user exit is EXIT_SAPLV60B_004, but since we have no experience with the include ZXVVFU04, we don't know how to write the enhancement...

existing code :

&----

*& Include ZXVVFU04

&----

The following is moreless the logic we would like to get in this code:

IF BKPF-BLART = 'RV' AND BSEG-KOART = 'D'

BSEG-SEGMENT = 'BSEG-AUFNR'

Can anybody please give me a hint on how to write the code in this include?

Thank you very much in advance!