Suhail, One of the ways is to use a network simulation software such as OPNET or NetSim (which I have used), and simulate the attack using that. The link https://tetcos.com/file-exchange.html has some codes and documentation for a DDOS Attack in IOT, related to NetSim.

Shubham Gupta Thanks! I checked the link and there seems to be a lot files. I could not understand which files do I need to make a DDoS attack.

I cannot find NetSim application. Where can I download it freely?

NetSim is not a free tool. I think your university can purchase it at discounted academic prices.

Article Communication security in internet of thing: Preventive meas...

Some researchers used Cooja Simulator for WSN and IoT and the previous paper is an example.

http://www.contiki-os.org/start.html