Deleting your Gmail account is a permanent decision. Once you delete your account, you will not be able to get it back or any of the data associated with it,
To delete your Gmail account, follow these some steps
Go to the Google Account website and log in to your account
Click on the "Data & privacy" tab.
Scroll down to the "Data from apps and services you use" section and click on "Delete a service
Under "Choose a service to delete", select "Gmail
Click on "Delete service
Enter your password and click on "Next
Review the information about what will be deleted and click on "Delete Gmail