In Settings → Security → Form Password Protection you can set a password for your form. Share it with your target audience and forbid access for other submitters. Set the button to On, type a password in both textbox fields and you’re ready to go. To make your form available to everyone, deselect the option.
This option is available on paid plans only, such as Gold, Platinum or higher.
Note: The password cannot exceed more than 15 characters.