Installing the Watch Link phone app should automatically trigger a download of the Watch Link watch app to your Apple watch. If this fails, the watch app can be manually downloaded in two different ways. 

Download from the Watch app

1. Open the Watch app on your phone
   
2. Scroll down to 'Available Apps'
   
3. Install the Watch Link app
   

Download from the Watch's App Store

1. Open the App Store on your Apple watch
   
2. Type ‘Watch Link heart rate’ app in the search bar
   
3. Select Install