https://wccftech.com/enable-ecg-on-apple-watch-for-unsupported-regions/

The ECG feature in Apple Watch Series 4 and later is only available in 35 countries and regions around the world, even though the watch is sold in a lot more locations. Luckily, thanks to a new jailbreak tweak called ECG Enabler, you can now enable ECG on your Apple Watch anywhere in the world. Here is what you need to do.

Before you start the guide, make sure that your iPhone is on iOS 13.5, and Apple Watch is on watchOS 6.2.5. It goes without saying that your iPhone should also be jailbroken using unc0ver or checkra1n, on iOS 13.5. Also, only Apple Watch Series 4 and Apple Watch Series 5 support electrocardiogram readings, older watch models do not have the required hardware.