Hi Ravi,
When we add a field to data source extracts structure. we need to write a logic to fill that filed.
here we have two ways to fill the enhanced field.
1. CMOD, EXIT_SAPLRSAP_001, in include program we need to write a logic.
2. BADI enhancement. SAP give one is - RSU5_SAPI_BADI.(search about badi more from Google " Enhancing DataSources with BADI")
for above two, you need take abaper help and do it accordingly.
Once you done coding, at RSA6, you need to unhide added field.
Thanks