How can I obtain the ECG app in Australia?

https://support.apple.com/en-ph/HT208955

• The ECG app is available in the United States, Puerto Rico, Guam, and the U.S. Virgin Islands.

All we can do for the meantime is to wait until Apple release it, because there are few things that Apple needs to work on in each country, like permit etc to release the feature, plus it depends on the law covering your region.

There is another option besides waiting: get the Apple Watch series 4 from the US instead of buying it in your country. That's what I did (but not specifically because of ECG) and I already have ECG without needing to wait until it gets approved here in Mexico (if it ever does get approved, because Mexico is usually one of the last countries where apple launches everything except for the new iPhones every year).