Currently there is no direct way with which a downgrade can be done. I managed to do the downgrade by downloading Android Studio 3.0.1 from here and then running the installer. It will prompt whether to uninstall previous version, and when you allow and proceed, it will remove 3.1 and install 3.0.1.
You need to ensure 3.1 is not running in background i.e. Close the Studio 3.1 application.