ECG doesn't come up when searching the browse tab in Apple health app

1. Open the Health app on your iPhone, then follow the onscreen steps to set up ECG.
2. If you don’t see a prompt to set up, tap Browse at the bottom right, tap Heart, then tap Electrocardiogram (ECG).

If you don't see Heart, the first (and simplest) thing to try if something isn’t working right is to restart your Apple Watch and its paired iPhone. If necessary (device not responding), try a forced restart. Both methods can be found here:

How to restart your Apple Watch - Apple Support

Restart your iPhone - Apple Support

If that doesn't help, the next steps would be to unpair and pair your watch again and restore from the backup just created. This should result in no loss of data. It deletes all temp and corrupted files and re-indexes the file system.

Unpair and erase your Apple Watch - Apple Support

Set up your Apple Watch - Apple Support

If that doesn't help, your best option may be to make an appointment at the Genius Bar in an Apple Store near you and let them look at it. Or use the online Apple support option. Either way:

Genius Bar Reservation and Apple Support Options - Apple