How can I enable face id for my messages application?

Hello, mahi49.

Are you trying to set up Face ID for your iPhone 11? If so, these steps explain how to do that: Use Face ID on your iPhone or iPad Pro - Apple Support. Follow these steps:

First, "make sure that nothing is covering the TrueDepth camera or your face. If something is obstructing your nose or mouth — like glasses or a face mask — you might be asked to temporarily remove these items during setup. You can also use Face ID with face masks if you use iPhone 12 or later with iOS 15.4 and later. Face ID works best when your iPhone or iPad is approximately 10–20 inches from your face."

To set up Face ID:

1. "Go to Settings, then tap Face ID & Passcode. If asked, enter your passcode. If you didn’t set a passcode, you’ll be asked to create one to use as an alternate way to verify your identity.
2. Tap Set Up Face ID.
3. Hold your device in portrait orientation, position your face in front of your device, then tap Get Started.
4. Position your face inside the frame and 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. Tap Done."

Once that is done, you will be able to choose features that you want to use Face ID by going to Settings, then tapping Face ID & Passcode.

Let us know if we can help with anything else at all or if this doesn't settle your issue. Thanks and have a fabulous day!