Apple id verification
Trusted phone number not in use how to change the number
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You need to change the number on your Apple ID. After the change, allow up to 24 hours for the change to sync. Before trying to make the change, sign out of Messages/FaceTime on all devices/computers.
If you need a verification code to sign in, see if anything here helps. If necessary, you can use account recovery as explained in the link at bottom of the article.
Verification code - how to get one and sign in with two-factor authentication.