The watch does not automatically update weather data. You need to connect the watch to the app to synchronize weather data. You can update the weather by following these steps:
1) Make sure that you have set the city for which you need weather data. In the app, go to Profile > Amazfit T-Rex 3 > Weather settings.
2) Return to the home page of the app and pull down to sync data. After data synchronization is complete, enter the weather screen to view weather data for the city that you set.