Like the last platform, we still have the web app running, so if you had that installed; delete it from your Home screen and reinstall again.
If you didn't have it running before, it's definitely worth adding to your phone or tablet, as you will get notifications of any watched topics, DMs, post replies, etc, sent directly as notifications.
To install or reinstall on the newer platform, make sure you are logged in on your browser; then click the three lines at the top left of the site. It...