Good news for those who live in Singapore and have set your phone to Singapore English as a language, you should start seeing Assistant soon when you tap and hold the home button on your phones, instead of the Google Now on Tap / Screen Search that was before it. This should work on all Android phones with 6.0 and above.
Singapore English joins 5 other English variants in being supported by Assistant: US, UK, Australian, Canadian, and Indian. However, unlike some of these, it isn't yet available through Assistant on other devices like TV and Home.
Source : Google