This article explains how to add Google Assistant to your iPhone on top of Siri, so you can open Google Assistant by saying, "Hey Siri, Hey Google." The instructions in this article work for iOS 12 and later.
How to Use Google Assistant on iPhone
Before we dive in, make sure Siri is enabled on your phone. In most cases, Siri will be on by default, but if you need to turn it on, open Settings > Siri & Search and toggle the Listen for “Hey Siri” slider to on.
On your iPhone, open the App Store and search for Google Assistant, then tap Get > Install. If prompted, enter your Apple ID.
Open the Google Assistant app and sign in or continue with a Google account. You’ll see a message about Google Partners working with your Assistant. Tap Continue.
