@VishalMali 

Hi, may I know if you want to connect the Archer D9 to the main router by cable? Your main router is working well, right?

If so, please connect the LAN4/WAN of the modem to the router's LAN port by cable.

Then, follow the instruction to enter the management page of the modem. https://www.tp-link.com/support/faq/1730/

You can follow the below instruction to set up the Archer D9.

Click Advanced on the top. On the left side, Click Operation Mode. The modem router supports two modes: DSL Modem Router Mode and Wireless Router Mode.

Choose Wireless Router Mode and then click Save. A reboot window will show up, click on YES. After reboot, go to Network--Internet, choose dynamic IP, save it.

If you want to change the IP address of the modem, please follow the instruction to achieve. https://www.tp-link.com/support/faq/873/

Actually, we have the local team in India. Here is the contact information: https://www.tp-link.com/in/support/contact-technical-support/#Hotline-Support

At last, I don't understand what you are looking for. 'I need the software for the same'

Could you please explain it more clearly for us?

Look forward to your reply.