How to set a passcode lock?
To set a 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. Select "Turn Passocode On".
6. Set a passcode.

Note: Once you've set a passcode, the next time you tap on the Bigin app icon to open the app, you'll need to use the passcode to enter the app.