Can I reprogram Face ID? It doesn't work since I dyed my hair.

For most users, Face ID will continuously learn as they change. If you have an appearance that can look vastly different, you can set up an alternate appearance so Face ID still recognizes you.

To set up an alternate appearance:

1. Go to Settings, then tap Face ID & Passcode. If asked, enter your passcode.
2. Tap Set Up an Alternate Appearance.
3. Look straight into your iPhone or iPad and place your face inside the frame.
4. Gently move your head to complete the circle. If you're unable to move your head, tap Accessibility Options.
5. When you finish the first Face ID scan, tap Continue.
6. Gently move your head to complete the circle for a second time.
7. When Face ID setup is complete, tap Done.

Hello,

Here's the support page for FaceID. It includes a link for resetting it if you need to:

If Face ID isn't working on your iPhone or iPad Pro - Apple Support

Hope that helps!