How to change my recovery number?

Hi there!

Are you referring to the trusted phone number where the 6 digit verification codes are beìng sent to? If so, you would first need to have access to your Apple ID before adding or changing your trusted phone number.

You can find the steps under the "Manage you trusted phone number" section in this article

Two-factor authentication for Apple ID - Apple Support

If you no longer have access to your Apple ID to change the trusted phone number, you can try reaching out to your carrier and ask them if they can still provide you another SIM card with the same number so you can still get the codes or you can request for an account recovery at https://iforgot.apple.com/password/verify/appleid

How to use account recovery when you can’t reset your Apple ID password - Apple Support

Account recovery will work if you can still recall what the trusted phone number is

If you are referring to the Recovery key, you can generating a new one

How to generate a recovery key -

Apple Support

If you need further help, please Contact - Official Apple Support

Hope that helps!