Hi Bizzyness,
Sounds like you previously set up a Recovery Key - Set up a recovery key for your Apple ID - Apple Support. This is a 28 character code that is provided once to you and you’re supposed to store it securely to later prove who you say you are. This can be for unlocking your account in the event you forgot your passwords. You will need to enter this key before changing settings.
Use a recovery key
To change your Apple ID password, you need a trusted device (with a passcode or password) or your recovery key.
If you don't have access to a trusted device or you're locked out of your Apple ID, you need to provide your recovery key to reset your password and regain access to your account.
When you change additional information about your Apple ID (for example, if you add a trusted phone number), you might be asked for your recovery key.
You can disable this setting, but you will need your Recovery Key to turn it off. Recovery Key are more secure, however for the majority of people, I always recommend using the Recovery Contact option.
If you forgot your Recovery Key you will need to do the following:
As long as you remember your Apple ID password and still have access to one of your trusted devices, you can sign in and create a new Recovery Key.
Go to your Apple ID account page.
Sign in with your password and trusted device.
In the Security section, click Edit > Replace Lost Key.
Keep your new Recovery Key in a safe place. Your old Recovery Key won't work anymore and you can't use it to reset your password or access your account.