how do i delete an unused email account?

How Can I Delete an Old Account If I Forgot My Email and Password?

Select the Data & personalization option from the menu on the left.
Scroll to the “Download, delete, or make a plan for your data” section and click the “Delete a service or your account option.”
Click Delete a service.
Enter your password.
Click the trash bin icon next to the service you want to remove.

Delete Previously Used Email Addresses from Gmail Auto-Complete List