In case you have a previous phone with two-step authentication, you can deactivate its setting by yourself and reconfigure it with a new phone.
Please follow the steps below to deactivate.
1．Launch the authentication app you downloaded such as Google Authenticator or IIJ Smartkey etc.
2. Select "Settings"(設定) from the menu, and press the "Release"(解除) button under "Two-Step Authentication".
3. Enter the 6-digit code displayed on the authentication application in the "Two-step verification code*" field on the "Two-step verification settings" screen.
If you have set up SMS verification, you will also be asked to enter the "SMS verification code". Please obtain and enter the "SMS verification code" with the longest expiration date first, and then enter the "two-step verification code".
4.Press the "Cancel Request"(解除リクエスト) button.
Please note that the "two-step verification code" and "SMS verification code" each have an expiration date of several tens of seconds, so please process the request promptly.