You can check your  ID in Account Settings.

How to check

1. Sign in to your account.

If you are unable to log in, please refer to Troubleshooting for signing in to your account. 

2.After signing in, access [Account Settings].

PC

Click the display name in the upper right corner of the screen and select [Account Settings].

Smartphone

Tap the menu button (3 lines) in the upper right corner of the screen to open [Account Settings]. 

3.Confirm “User ID” in Account Settings.