If you have lost your Google account user ID, you can restore your ID on the Google homepage.
How to restore your Google account user ID.
1. Visit the Google homepage (www.google.co.kr) and select “Sign in”.
2. Click “Need help?” text.
3. Select “I don’t know my username” and click the Continue button.
4. Select “Enter your recovery email address” and input each field.
5. Select the check box before “I am not a robot” and select the images presented on the screen and click Verify.
6. Input the password displayed on the screen and click Verify.
7. Click Submit to receive the Google account information via the e-mail address you have input in the recovery e-mail address. Log in to the recovery e-mail account and check the information e-mail from Google, and restore your Google user ID according to the instruction.