*First, make sure you have enabled Touch ID for your iPhone. (Click here for an Apple Support tutorial.)
1. Tap the three-line icon in the top left.
2. Tap the "Settings" option.
3. Tap the "Touch ID" toggle switch on.
4. Tap the "Lock After" section to edit the time out for the app.
5. Select your preferred "Lock After" time.
You will now be prompted to enter your Touch ID every time you access the app.
*Note that Touch ID works only with iPhones 5S, 6/6+, 6S/6S+ or later.