How can I add memory to this chatbot? Langchain and Qdrant were used

Question

I'm trying to add memory to this model that works using langchain and Qdrant I tried adding Conversation Buffer But there are problems, can anyone help me with this? Can I add streamlit session state Or any of the types of memory in Langechen

from dotenv import load_dotenv
import streamlit as st
import os 
from langchain.vectorstores import qdrant
from langchain.embeddings.openai import OpenAIEmbeddings
import qdrant_client
from langchain.chat_models import ChatOpenAI

from langchain.chains import RetrievalQA
from langchain.llms import openai

def get_vector_store():
    client= qdrant_client.QdrantClient(
        os.getenv('QDRANT_HOST'),
        api_key=os.getenv('QDRANT_API_KEY')
    )
    embeddings= OpenAIEmbeddings()


    vector_store = qdrant.Qdrant(
        client=client,
        collection_name=os.getenv('QDRANT_COLLECTION_NAME'),
        embeddings=embeddings,
    )
    return vector_store

def main():
    load_dotenv()
    st.set_page_config(page_title="Ask Your Data")
    st.header("ask what do you want to know")
    
    vector_store= get_vector_store()
    


    qa= RetrievalQA.from_chain_type(
        llm=ChatOpenAI(temperature=0.7),
        
        chain_type="stuff",
        retriever=vector_store.as_retriever()
    )

    
    
    user_question = st.text_input("write your Question")

    if user_question:
        st.write(f"Question: {user_question}")
        answer= qa.run(user_question)
        st.write(f"Answer: {answer}")
if __name__ == '__main__':
    main()