What Should I Do If I Forgot My Recovery Key?

You may be able to reset your Apple ID password by using a trusted device or phone number, check this article:

...

If you forget your Apple ID password, you can try to regain access using your trusted device protected by a passcode. Or you can use your recovery key, a trusted phone number, and an Apple device to reset your password. Make sure the device is running iOS 11 or macOS High Sierra or later, and be sure to enter the complete recovery key including upper-case letters and hyphens. Learn more about what to do if you forget your Apple ID password. 

If you decide to stop using a recovery key, follow the steps above on your iPhone, iPad, or iPod touch, and slide to turn off Recovery Key. On your Mac, click Turn Off in the Recovery Key section.

...

copied from: How to generate a recovery key - Apple Support

See -> Two-step verification for Apple ID -> Two-step verification for Apple ID

👉 scroll to & read -> What if I lose my Recovery Key?

You can sign in to your Apple ID account page and create a new Recovery Key using your Apple ID password and one of your trusted devices.

1 Go to appleid.apple.com/uk.

2 Sign in with your password and trusted device.

3 In the Sign-In and Security section, click Recovery Key > Change Recovery Key.

Keep your new Recovery Key in a safe place. Your old Recovery Key won't work any more and you can't use it to reset your password or access your account. If you can't see Recovery Key in the Sign-In and Security section, then you are not using two-step verification. 

FYI: Write down your recovery key and keep it in a safe place.