Apple has shipped an update for watchOS just for the Apple Watch Series 3, with watchOS 7.0.3 fixing issues for that particular Apple Watch model.
Released on Monday, the update is only available for the Apple Watch Series 3, with the Apple Watch Series 4 and later continuing to use watchOS 7.0.2. The update appears to be a targeted fix for problems just for that model.
The release notes for watchOS 7.0.3 states it contains improvements and bug fixes, "including an issue where Apple Watch Series 3 may unexpectedly restart for some users."
It is unclear if an update for watchOS 7.0.3 will be made available for other models, as Apple is currently running beta tests on watchOS 7.1. It seems likely that Apple will issue 7.0.3 for other models if there are any other issues that need fixing, that can't wait for the watchOS 7.1 release.
Users of the Apple Watch Series 3 can update their devices by opening the Watch app on their paired iPhone, then tap the My Watch app, followed by General then Software Update. Once downloaded, the iPhone may ask for a passcode before installing it to the Apple Watch when the wearable device is charging.
Alternately, the update can be applied on the Apple Watch directly, by opening the Settings app, tapping General, then Software Update. If an update is available tap Install then follow the onscreen instructions.