Siri wake

To use Hey Siri ask in a complete sentence: “Hey siri, what is tomorrow’s weather?” Do not wait for Siri to respond to Hey Siri before completing your request. If you pause Siri will wait a second or two, then say “Uh huh”. Sort of like for friend would if you said “Hey Bill” and then paused. Likewise if you hold the Side button to wake Siri; don’t wait for a response, just start talking.

Retrain Siri with your voice

Go to Settings > Siri & Search, turn off Listen for “Hey Siri,” then turn on Listen for “Hey Siri” again. To change Siri accessibility settings, see Use accessibility features with Siri on iPhone.

Change Siri settings on iPhone - Apple Support (IN)