Head to your Virgin Money Mobile Banking app and on the sign in screen, tap on "Forgotten your passcode?". Then follow the on-screen steps to reset your passcode.
If you have biometrics set up for your app, this skips the sign in screen where the 'Forgotten your passcode?' link is. You'll need to turn biometrics off for your app or stop it from automatically signing you in. You'll then be able to see the sign in screen and reset your passcode.
Once you have updated your passcode go back to your Virgin Money Credit Card app and try again.