How to Install Form Builder
Create new or open any of your Google Form.
Click on the 3 vertical dot button (top right corner of your Form) .
Now click on "Add-on" option from the menu
search for "Form Builder"
Select Form Builder from the search result and click on Domain Install or Individual Install
It will take you to the Authentication window and select your account
click Allow that will complete your Authentication process.
That's It. your installation process is Completed.
Click on "DOMAIN/INDIVIDUAL INSTALL" button
Follow the steps above.