Redirect within controller!!!

Hello!

I found a chatbot to add to my site and it works but the issue is that it redirects to my landing page (which was the original welcome message page). Im believe I have to change something within the contoller but dont know where. Trying to fix it that when I hit submit instead  of going to another page the comment/words are in the message board. Here is the git Im using:

https://github.com/afiefsky/chatapp-codeigniter-ajax

Where do I make the change?