In Settings > Touch ID & Passcode, you can make your device life easier by customizing some of Touch ID’s options:
Touch ID supports up to five fingers
Add fingers for other situations, like holding your device in a different hand, or unlocking when it lays flat on a surface.
You can allow other people to access your device
But be extremely careful. If you allow Touch ID for making purchases, those other people can essentially make purchases on your device with your Apple ID and credit card/PayPal. But this can be useful for loved ones who need help using their device, or to let your children into your device (but perhaps you could disable Touch ID for making purchases)
Disable Touch ID’s use for some services
In the Touch ID Settings page, you can change its ability to control some services, including unlocking your devices, Apple Pay, and making purchases in the App and iTunes Stores.
Verify which fingers Touch ID understands
While on the Touch ID Settings page, press a finger on the Home button (but don’t click it) to verify whether it’s registered with Touch ID. If that finger is registered, its Touch ID entry will highlight. In my screenshot below, my right thumb is verified.
Rename, delete registered fingers
Tap a finger entry in Touch ID to rename or delete it.