Changing My trusted number

Two-factor authentication for Apple ID - https://support.apple.com/HT204915 "You can manage your trusted phone numbers, trusted devices, and other account information from your Apple ID account page." --> https://appleid.apple.com/

You need the code to sign into your Apple ID. 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.