First, tap the "Settings" button on the main wallet page.

Then tap "Passcode and Touch ID" or "Passcode & Face ID" depending on your device's biometrics option.

You will be asked to enter your passcode on the following page.

Then, tap "Change Passcode". From here, you will be able to enter a new passcode, or change the style of code by tapping "Passcode Options". From the options, you can choose either a 4-Digit Numeric Code or a Custom Alphanumeric Code.

From the main "Passcode and Touch ID" or "Passcode and Face ID" page, you can tap the button to enable biometrics unlocking. You will then be prompted for your biometric input (facial recognition or fingerprint).