code: def deactivate_mfa_device(self, user_name, serial_number):
          
          user = self.get_user(user_name)
          if serial_number not in user.mfa_devices:
              raise IAMNotFoundException(
                  "Device {0} not found".format(serial_number)
              )
  
          user.deactivate_mfa_device(serial_number)
docs: Deactivate and detach MFA Device from user if device exists.