You can use Wi-Fi as an alternative to the mobile network when establishing an internet connection. This way your smartwatch doesn't use mobile data.
Slide your finger downwards starting from the top of the screen.
Press the settings icon.
Press the indicator next to "Wi-Fi" to turn on the function.
Press Add network.
Press the required Wi-Fi network.
Press Enter on watch.
Key in the password for the Wi-Fi network and press the confirm icon.
Press the crown to return to the home screen.