You need to learn more on either one of the widgets. ECG or BP widget on the watch. Once you press learn more scroll down to download app. it will then show up on your phone to download. If you haven't added the widgets add them to the watch from galaxy Wear under widgets. hope this helps.
Could try 1) Check in Wearable app that your watch software is up to date , then 2) Open the Blood Pressure app on your watch and see if it refers to the Health Monitor app and then gives a link on phone ( or in the Wearable app on phone ) to download
I can't remember exactly how I did it but was something along these lines