ChatEngine

Try chat engine, It'll make your bot to have previous conversation and use it for answering new queries: https://docs.llamaindex.ai/en/stable/module_guides/deploying/chat_engines/root.html#concept

Any docs on what the basis of this is. I want to understand how it was built

Yeah I have shared the doc link for Chat engine above. If you want to check the code here it is: https://github.com/run-llama/llama_index/tree/main/llama_index/chat_engine

You can check different mode of Chat engine and check the code based on that mode.