If Siri wasn’t activated while setting up your iPhone, you can activate it by opening Settingspressing Siri & Search and then turning it on. You’ll want to ensure Press Home/Side Button for Siri is toggled on.

Siri is your personal assistant and can be used to control certain functions on the phone by using voice commands. To access Siri, press and hold the Side button (or Home button if your device has one) for a few seconds until the Siri interface appears and your device asks, “What can I help you with?”