The ECG feature on your watch is a white circle with a red heart beat line on it. On my watch, it’s top left where you see all apps (by pressing the crown button).
When taking the ECG reading, you need to be sitting and you keep one finger on the crown for the 20 or 30 seconds it takes to get a reading.
If you want more general heart data on your watch, you need the red circle with a heart symbol on it.
If you want to view data on your iphone, use the ‘Health’ App (standard app from Apple). All sorts of interesting stuff in there.