I am trying to use my fingerprint but Touch ID is not working.

Try these:

1. Make sure that you have the latest version of iOS or iPadOS.
2. Make sure that your fingers and the Touch ID sensor are clean and dry.* For the Touch ID sensor, use a clean, lint-free cloth to wipe off any dirt or debris.
3. Your finger should cover the Touch ID sensor completely, touching the surrounding metal ring. While Touch ID is scanning, you shouldn't tap too quickly or move your finger around.
4. If you're using a case or screen protector, make sure it doesn't cover the Touch ID sensor or the surrounding ring.
5. Go to Settings > Touch ID & Passcode and make sure that iPhone Unlock or iTunes & App Store is on, and that you've enrolled one or more fingerprints.
6. Try enrolling a different finger.

If it doesn’t work, take it to an Apple Retail Store or Apple Authorized Service Provider, or contact Apple Support.

If you took your iPhone to a 3rd party repair shop that is not affiliated with Apple and cannot get Apple parts, and they replaced your screen and your Touch ID, or inadvertently disconnected your Touch ID while replacing the screen. Touch ID will no longer work.

Have you had this iPhone service at a 3rd party repair shop?