import streamlit as st

def update_text_area():
    # Your code to update the value of the text area
    st.session_state.text = "Updated text"

if "text" not in st.session_state:
    st.session_state["text"] = ""

text_area = st.text_area("Enter text", value=st.session_state["text"], height=200)

# Button to trigger the callback function
if st.button("Update text"):
    update_text_area()