Carrot forms have a feature to let your site visitors bypass a Landing Page, or Page if they have already completed the form. This is useful for requiring an opt-in to see a specific page or other content on your website.
To enable this for a form, simply
Edit the form in your site’s admin
Click on “Confirmations” under “Form Settings”
Edit the default confirmation
Make sure the confirmation is set to a type of “Page” or “Redirect”
Check the box for “Allow Return Access”
That’s it! Now once a visitor has filled out this form, they will automatically be redirected to the confirmation page rather than having to fill out the form again.