LampO is an independent watch app. That means nothing is installed on the phone. You don't even need a phone to download or use the app.
- On the Apple Watch, Open the App Store application
- Search for Lampo VeSync
- Click the cloud download icon
- it would appear if you have downloaded it before
- you will see "open" if it is already installed
- you will see price button if you have purchased with a different account than the one you are currently signed in
- Now just open the app and log in as you would normally sign in through the iPhone VeSync app.
If you open the App Store application FROM THE PHONE, instead of the watch, you are going to see something like the following image. That means you own the app, however, it doesn't necessarily mean you have installed the app on the watch. In order to verify that, from the phone, open the Watch App and check that it is part of the installed apps.