Open the Gmail app or go to Gmail in a browser
Sign in to the Gmail account you want to delete
Click your profile picture
Select Manage your Google Account
Go to Data & privacy
Scroll to Data from apps and services you use
Select Download or delete your data
Click Delete a Google service
Sign in again if prompted
Find Gmail in the list
Click the delete icon next to Gmail
Enter an email address to use for other Google services
Verify the email address
Check the confirmation email sent to that address
Open the email and click the confirmation link
Follow the on-screen steps to complete deletion