step 1: open the setting app step 2:touch touch id...
TRANSCRIPT
How to Change to a Complex Passcode?
Step 1: Open the Setting App
Step 2:Touch Touch ID & Passcode in the left menu
Step 3: Touch Turn Passcode On
(If you had a numerical passcode you will have to enter it.)
Step 5: Choose Custom Alphanumeric Code
You can use letters, numbers, and symbols. Make sure to remember it!
Step 4: Touch Passcode Options