How do I change my number for Apple ID

If you trying to change the phone number associated with your Apple ID, 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.

Apple ID - Manage            

https://support.apple.com/en-au/HT202667

See Use your mobile phone number as your Apple ID https://support.apple.com/en-us/HT207944#change-appleid See the heading Change your Apple ID to a different mobile phone number.