How to Undo a Sent Email in Gmail (Guide)
Step #1: Open mail.google.com in your browser. Login with your Gmail id and password.
Step #2: Once you are logged in click on the gear icon located on top right corner of your screen.
Step #3: Now from the drop down menu click on settings.
Step #4:In settings search for Labs and click on it, there you’ll see several features. Search for UNDO send feature and enable it.
Step #5: Now click on Save Changes.