How to Enable ECG Feature in Recently Bought Watch Series 5 from eBay Deal - US Stock ($399) ?

Hello Everyone, Looking for the suggestion on how to enable ECG feature in apple watch(US Stock) bought from recent ebay plus deal.

I already tried couple of things:
1. Tried to change Region in Watch Application on iPhone
2. Tried to change Language
3. Restarted watch and iphone

But still can't see app for ECG, Please help if someone already enabled this feature.

Thanks in Advance.