Most of the issues that you may encounter with your Apple Watch can be solved using one of the below procedures.
How to Force Quit an App
If an app is unresponsive (blocked on the loading page/status), you can force it to close using the below procedure. Hold the Side button to bring up the Power menu. Hold the Side button again to close the app and go back to the homescreen of your device. You can try to launch the app again.
You might want to force reset/reboot your Apple Watch in the situations where the device has become unresponsive, when apps have become unresponsive and won't close (freeze) and when you are unable to connect to Wi-Fi or sync data with your iPhone.
To force restart your device simply press hold down the Digital Crown along with the Side button until the screen goes black. This procedure bypasses the Power menu causing the device to take a longer time to boot.
Restore to Factory settings (Reset)
Use one of the below procedures to reset your Apple Watch to its default settings. Warning: All your personal settings, downloaded apps and data will be erased.
From the Apple Watch: Go to Settings > General settings > Reset > Erase all Content and Settings and enter your passcode when prompted.
From the Apple Watch app: You can also use the Apple Watch app installed on the paired iPhone to reset your Apple Watch. Open the app and go to My Watch > Settings > General > Reset and tap on Erase all Content and Settings.
Once the Apple Watch is restored, you can pair and sync it again with your iPhone.
Keep the Apple Watch software up- to-date
Make sure that latest software is installed on your Apple Watch to benefit from the latest security features, performance improvements and bug fixes. You can perform a manual update directly from your iPhone using the Apple Watch app. Just make sure that both devices are close together and that your iPhone is connected to the Internet (Wi-Fi). You should also verify that the Apple Watch has at least 50% battery charge and is connected to its charger during the update procedure.
The update procedure can be achieved in a couple of easy steps. Open the Apple Watch app and go My Watch > General > Software Update. The small number displayed next to Software Update indicates that an update is indeed available for download:
Enter the passcodes for your iPhone and Apple Watch when prompted and simply wait for the update file to be downloaded and installed on your device.