How to Use Passcode & Fingerprint on your iPhone
You may have set up Touch ID when you set up your iPhone. If not, follow these steps to add your fingerprint or that of someone else, like a child or significant other.
Tap Settings→General→Passcode & Fingerprint→Fingerprint.
If you previously assigned a Passcode to your iPhone, you have to enter it before you can access the Fingerprint set up.
Tap Add a fingerprint.
Place your finger, or thumb, on the Home button.
The fingerprint on screen begins to redden as the whorls and swirls of your finger are memorized.
Lift and replace your finger on the Home button and roll it around so the Touch ID sensor can memorize the edges of your finger.
When your fingerprint is successfully read, tap Fingerprints in the upper left corner.
Choose when you want to use your fingerprint to authorize actions by tapping on Passcode in Lock (to use Touch ID to unlock your iPhone) and/or App and iTunes Store (to authorize purchases with Touch ID).
(Optional) Tap Edit, and do one of the following:
Name the fingerprint: Tap the fingerprint and then type a name, such as “Barbara’s Index” or “Lucy’s Paw.”
Delete the fingerprint: Tap the red and white button next to the print you want to delete, and then tap Delete.
Tap in the upper left corner or swipe right until you reach the main Settings screen, or just press the Home button to return to the Home screen.