Just like with any other platform, sometimes Apple Watch apps will freeze or have bugs. Thankfully, watchOS 3 includes a quick way to force-quit an app from your wrist, allowing it to start fresh.
With limited buttons and screen real estate, force closing an app on the Apple Watch is not quite as simple as it is on an iPhone, iPad, Mac, or even Apple TV. But it's still possible with a pair of button presses.
With the problematic app in question open, simply hold the side button for about two seconds. This pulls up the usual "power off" screen.
From here, press and hold the Digital Crown in for another couple of seconds. The buggy app will then immediately close, returning the user to the Apple Watch's "honeycomb" home screen.
To restart the app, tap on it from the home screen. It should now have a fresh start and will hopefully let you bypass any crashes or glitches.
For more, see everything you need to know about watchOS 3 for Apple Watch.