How to recover an account when a user entered a wrong email during signup?

1. How can I recover my inaccessible Gmail account?
2. What to do if email ID is already exists?

How can I recover my inaccessible Gmail account?

Go to the account recovery page. Answer the questions to the best of your ability. Tip: There's no limit to the number of times you can attempt to recover your account. To recover your Google Account or Gmail, follow the steps on the account recovery page.

What to do if email ID is already exists?

When an admin tries to add a registered user who belongs to another organization then an error message will pop up, saying that this email id already exists. Solution: You can ask that user to close the account and request the System Administrator to add this user.