Use the ItGupLine routine to access and update a specific row in a table:
void SAP_API ItGupLine(ITAB_H itab, unsigned line);
This routine returns the address of the requested line (specified by line). ItGupLine functions just like ItGetLine, except that you may update the data at the returned address.
The corresponding ABAP operation is Read Table... Index..., Modify...
This function is defined in SAPITAB.H.
See also ItGetLine, ItCpyLine and ItPutLine.