Hi Avinash,
Please follow the below step to edit the Excel Addin:
1 Open Exel sheet and prest Alt+F11, you will get VBA code window.
2 in the left side of the window you will see the list of VBA projects.
3 Click on VBAProject(TDExcelAddin.xla)
4. Password is "tdtdtd"
you will see all the TdExcel addin OTA code, you can modify as per your requirement.
Thanks,
Ramesh