You can restrict access to your form via a password. Only people who have this password will be able to submit the form. Select the option and enter the password of your choice in the password field. Save the changes, and your form will now be password-protected.
How to enable this option
Open the form and click on the Settings tab.
Click on Access control in the left sidebar.
Select The form is password protected. Anyone who has the password can submit the form.
Type the password of your choice in the Password field.
Click Save changes.
Publish the form so the new setting takes effect.
Share the password with the people you want to give access to.
To explore the other access control options, see Managing access to a form.