login into google account that is linked to your Whatsapp account
Once logged in into Google Account , go to the top right corner, click on google apps image-> Click Google Drive Icon
Go to the Bottom left corner , look for storage and click on it.
Go to the right corner , look for Backups – >Click on it.
Look for whatsapp backup
Click on 3 dots[vertical] ->Will show “Delete backup” and “Turn off backup” Next Click on “Delete backup” to delete
Next will ask for confirmation -> Click on Delete button to get it deleted