What is the most elegant way to make a chain from langchain into a query engine/query tool for LlamaIndex, please?

Now it seems I could create a Query Engine, right?

Thanks!

I didnt setup bot to enable multi-round conversation, yet, but it seems this one will work, please correct me if wrong. https://github.com/jerryjliu/llama_index/blob/main/docs/guides/tutorials/building_a_chatbot.md