Changing the phone # that’s connected To Apple ID

my friend was asking something about her device.

her question was that she wants to change the phone number that’s connected to her Apple ID, but it requires a code that she should receive to the phone number that’s already connected. But the thing is that she doesn’t have access to that phone number anymore.

so does anybody know other way to change the phone number that’s connected to her Apple ID other than getting the code to the number that she doesn’t have access to anymore?