The update can now be downloaded via the included Watch app on iPhone by going to General> Software Update in the My Watch section of the app.
Your watch must have more than 50 percent power and be connected to a charger. Like most Apple Watch updates, it can take anywhere from 30 minutes to an hour to complete, so be patient.
Here are the complete release notes:
watchOS 7.0.2 includes enhancements and bug fixes, including:
Resolves an issue that may cause the battery to drain faster
Resolves an issue that prevented some users from accessing the ECG app in regions where it is available
The problem of draining the battery seemed to be particularly prevalent after watchOS 7 landed in September.