Sign in to your Google Account
Go to myaccount.google.com
Click Data & privacy
Scroll to Data from apps and services you use
Click Delete a Google service
Sign in again if prompted
Find Gmail and click the trash icon
Enter an alternate email address for signing in to other Google services
Check the verification email sent to that alternate address
Open the email and confirm deletion
Follow the on-screen steps to permanently delete Gmail
Download any important emails before deleting
If needed, delete the entire Google Account from the Google Account settings