How to enable Delta function Generic Data Sources with FM

Hi experts,

I have created Generic DataSource with Function Module and data is retriving to BI with full load sucessfully, but I want to enable Delta functionalty for the DataSources.

Historical data also comming every day it is effecting verymuch on performance and loads also.

I need inputs to enable Delta function for the datasource.

I have found one standard Function Module in form search but it is not working (RSVD_BW_GET_DELTA_DATA)

I could not able to intiallize by useing this FM.

Regards

Vijay