I forgot my Recovery Key

If you're using two factor authentication you basically cannot. If you're using two -step verification see the second section below.

From: How to generate a recovery key - Apple Support

- With two-factor authentication (the current security system) and an Apple device, you have the option to generate a recovery key to help improve account security.

- When you generate a recovery key, you can't use account recovery.

- "Using a recovery key is more secure, but it means that you’re responsible for maintaining access to your trusted devices and your recovery key. If you lose both of these items, you could be locked out of your account permanently."

- See the document for how to generate a key. Apple mobile devices and Macs only.

Use a recovery key

- 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.

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This method is for the older, Two-step verification for Apple ID - Two-step verification for Apple ID - Apple Support

This is the older security system.

This link will take you directly to the paragraph of the document dealing with a lost recovery key issue: Two-step verification for Apple ID - Apple Support :

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.

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 anymore and you can't use it to reset your password or access your account. If you don't see Recovery Key in the Sign-In and Security section, then you are not using two-step verification.