Hi Zeeshan,
Firstly you have to add new field to report's temp table (LedgerStatementTmp). Normally you have to add this field to the related query and then assign this field's value in processReport() method in DP class. But this report is more complicated than usual. If you look at the report you can see processReport() method is different than usual one. Additional methods and helper classes are used to calculate some fields and improve performance. The temp table is fullfilled in copyToReportTable() method. You have to add your new field to insert_recordset and select sections in this method. After that you can see your new field in visual studio and you can add new field to report design.
Best regards,
Sefa