To change your phone number on Messenger, open the app and select Home. If you see a conversation when you open the app, tap the Back button.
Tap your profile icon located at the top right or left of the screen (depending on your device). Next, select Phone and tap the cross icon when you select the phone number to remove it from the field.
Type your new phone number and tap Ok. Enter the security code you received by SMS to confirm the change, then tap Continue.