Some Apple Watches are showing the wrong time by an hour after the seasonal clock change, despite being expected to update automatically. Apple has attributed the problem to a bug. The issue does not appear to be widespread, but it could cause confusion, particularly for people who rely on their watch as an alarm.
The simplest fix is to restart the Apple Watch. Hold down the side button until the power slider appears, then continue holding it until the Apple logo comes back on screen.
If restarting does not help, switch to another watch face and then restore your preferred one using the Apple Watch app on your iPhone:
1. Open the app and tap “Face Gallery” at the bottom of the screen. 2. Choose any watch face and tap “Get.” 3. Open its preview and tap “Add to Watch.” 4. Return to the app’s main screen by tapping “My Watch,” then select your original face from the “My Faces” carousel. 5. Scroll down and tap “Set as current Watch Face.”
The temporary face change should correct the displayed time, after which you can return to your usual watch face.
Sources: Tom's Guide.