How to render html template from a callback function flask

From javascript , I am calling a fetch api which routes to the flask and in flask, I have a function that will get invoked at a interval of 15 seconds. From this callback function how to renderthe template. Earlier I was getting error that you are trying to render template outside the context. I resolved all those issues, Now I am not getting any error, render template line is also getting executed without any exception but in ui the page is not loading.