After the session state being introduced how do I create a reset button

I am now trying to create a reset button that allow the user to uncheck the boxes of all the checkboxes selected by user the Session state Example here streamlit reset app via button
is good but I am creating a reproducible app and hence need to use session state api but I am not able to do it.

What I tried was

if 'celcius' not in st.session_state:
    st.session_state.celsius = False

st.checkbox(
    "Temperature in Celsius",value=st.session_state.celsius
) 
a=st.button('Reset')
if a:
    st.session_state.celsius=False

but the checkbox does not change until I clear cache which is the last resort all I want is to give the user a freedom to reselect columns if he want to create different query (the button are query and reset query brings a set columns selected by user through checkbox and reset allows user to nullify selection and select again for different query)

no matter what I try like chaging it to true then false the or any combination even with callback does not reset the checkbox unless I clear cache