How to change your passcode lock?
Note: If the initial steps to set a passcode lock are incomplete, you will not be able to change your passcode lock.
To change your passcode lock
1. Open the Bigin app on your iPhone.
2. Tap the More 
icon at the bottom right of the screen.
3. Select Settings 
.
Under "Manage Privacy", you can find the title "Privacy & Security".
4. Tap on Privacy & Security > Passcode Lock.
5. Enter the current passcode.
6. Select "Change Passcode".
7. Enter your current passcode once more.
8. Follow the steps to change to a new passcode.
Note: Once you've set a new passcode, the next time you tap on the Bigin app icon to open the app, you'll need to use the new passcode to enter the app.