How to link to a html page in a different folder?

Hello everyone.
I have deployed a Deep Learning model using Streamlit. I created the whole web-app but now I want to create a forum page and add login sessions and link it to a database. So I am adding the latter features with a Flask web-app. With a hacky method, I was able to link the streamlit web-app in a html page using <iframe>.

Now I want to add a button saying “Link to Forum” which would link me to a forum.html file where all the flask magic happens. But I was unable to add a href for forum.html in streamlit web-app. Is there a way I can add a href for forum.html which is in the templates folder in my streamlit web-app?

Thanks for your help.