If you cannot sign into your account, don't have a valid way to get a verification code, and you mean doing this in order that you are able to add a number where you can get a code, it is a bit late to do that now. Your alternative is account recovery.
For information about how to use account recovery when you can’t reset your Apple ID password, click here --> How to use account recovery when you can’t reset your Apple Account password - Apple Support
- "Account recovery is a process designed to get you back into your Apple ID account when you don’t have enough information to reset your password." "If you use two-factor authentication and can’t sign in or reset your password, you can regain access after an account recovery waiting period."
The posts by forum contributor shoeluvr13 at these links provide additional detail about the account recovery process and what to do if you do not receive a text or call: Activation Lockout Issues - Apple Community and How can I reset my Apple Account password? - Apple Community . This thread illustrates the multi-step process My Apple ID is locked, how do I fix it? - Apple Community
From: How to use account recovery when you can’t reset your Apple Account password - Apple Support
"Check the status of your request
At any time, you can see how long it will be until your account is ready for recovery, or when more information will be available. Just go to https://iforgot.apple.com and enter your Apple ID."
From: How to use account recovery when you can’t reset your Apple Account password - Apple Support
"In some cases, you might be able to speed up the account recovery process or reset your password immediately by verifying a six-digit code sent to your primary email address. You might also be able to shorten the wait time by providing credit-card details to confirm your identity. If you’re given this option, an authorization request goes to the card issuer." - see the document for more details.
Cancel your request
If you remember your information and can sign in successfully, your wait period cancels automatically and you can use your Apple ID immediately.
To cancel a recovery request that you did not make, follow the instructions in your email confirmation.
When the wait period is over, Apple sends you a text or automated phone call with instructions to regain access to your account. Follow the instructions to immediately regain access to your Apple ID.
Posts purportedly detailing the process:
what if i dont have the nimber i use to s… - Apple Community
and
Locked out of another Apple ID because I … - Apple Community
When you can get back into your account you can then modify the trusted numbers.