If you have recently changed your phone number, mistyped your number on registration, or no longer have access to your number for any other reason, you have the option to update your phone number. To do so, first click on your profile picture. Then select the Information & security tab. Finally, select "Manage MFA". Once there, click "Update" next to your phone number:
Alternatively, you can select "Update" on the Multi-Factor Authentication page upon login.