How to fix "Requested runtime 'python-3.8.10' is not available for this stack (heroku-22)"?

I am trying to push my project on web using Heroku with the command "git push heroku master", but it shows me: Using Python version specified in runtime.txt remote: ! Requested runtime 'python-3.8.10' is not available for this stack (heroku-22) . Because I coded this app on python version 3.8.10, it is not supported by heroku-22. Is there any possibility of fixing it or downgrading the version or not?