It doesn't matter, Apple watch update system, you can no network, as long as your iPhone is connected to the network, download the upgrade package, you can connect the phone to update.
Method: Connect Apple watch and iPhone with Bluetooth, open the \"Watch\" App on iPhone, click General, Software Update, and download the installation package.
Note: When installing, the Apple watch needs to be placed in the battery compartment.
A phone hotspot can be used instead of wifi.