Do you see the Cardiogram app icon?
First, navigate to the “honeycomb” grid of apps on your Apple Watch, then try to find the Cardiogram icon, which looks like this:
If you can’t find it, then the next step is to check that Cardiogram is installed on your both your phone and watch.
Check that Cardiogram is up-to-date on your phone
Go to Cardiogram on App Store — if the button says “update” or “get”, then tap on it to make sure you have the most recent version of Cardiogram.
Check that Cardiogram is installed on your Watch
Open the Watch app on your iPhone, make sure you’re on the “My Watch” tab, and then check the list of apps (left). Cardiogram should say “Installed”. If it doesn’t, tap on the Cardiogram app name in the list of apps, and make sure that the “Show App on Apple Watch” toggle is green.
It may take a few minutes for Cardiogram to appear on your Apple Watch.
After a few minutes, try finding Cardiogram again on the honeycomb screen.