After you have installed the Google Forms add-on, it can be accessed and launched from any Google Form that is associated with your Google account.
forms.google.com and open any existing Google Form in your Drive. Or you can type
forms.new in your browser's address bar to create a new form where you wish to use the email add-on.
Open Google Forms add-on
Inside the Form editor, click the
Add-ons icon that resembles a puzzle piece as shown in the screenshot. Next, choose
Email Notifications for Google Forms from the list of available add-ons.
From the pop-up menu, click
Open App to launch the add-on as shown in the screenshot below.