The Discord desktop app automatically checks for updates when you open it, but you'll have to use your phone's app store to update the mobile app.

PUBG Mobile is a live-service, free-to-play, multiplayer game that frequently gets new updates. In it, you can expect new weapons, game modes, items, and more. If you are unable to download the update ...

To update Slack, you'll likely need to go to your system's App Store. Only Windows users can update from within the app.