Unable to access ECG on Apple Watch SE with iPhone 12 Pro

I have an iPhone 12 Pro and an Apple Watch SE. They are on the latest updates. They have been unpaired and repaired many times, but the health app on my phone always says this (in picture). I know my Watch can do ECG because it has the red ring on the digital crown but the app has never shown up after 3 years, even becoming the right age. How can I set this up on my watch?

[Edited by Moderator]

Original Title: Using ECG on iWatch