Over time, your voice may change, or Siri can't recognize your voice. Fortunately, Apple already thought of this and made it easy to update your voice. You can retrain Siri using these steps: 1. Go to Settings. 2. Tap on Siri & Search. 3. Toggle the Hey Siri switch off, then back on again. This should fix Siri if she isn't responding on any of your devices. If you're having trouble with only one device make sure the microphone is clean and free of debris and that your OS is up-to-date.