I think that by chat bot you mean an automatic response window for the user in a web page. That will be able to create cases and so on... If I am correct and you already have v7.4 or v8.x.x of the Pega Platform this is achieved using the webchat interface provided in the channel and interfaces menu entry of the application menu.
I have provided a screenshot so that you are able to find it. This is from v8 but is something similar to what you will find in v7.4.
Once you add a webchat interface you can configure it to recognize by exact match of commands the case types that you want to include in the conversation with the users. Within the cases you can include automations that interact with RDA, and RPA in case you have the need to do so. I have not tested the pega infinity Robotics topic but I know the are stating that is part of the cloud now, so it should be somewhere. Hope this helps, regards,