This article explains the setting of a form called "Remember me". You will be able to find this setting if you navigate to the form module placed on of the pages of your experience. 

How it works

Remember me is a form setting that provides the ability to recognize a user who has previously entered an experience. If the setting is enabled, experiences that accept Unlimited or Daily entries (user can enter repeatedly), will only ask for a user’s email. If a user is known, form fields that have been already presented to the user before will be hidden or shown, based on the individual field settings.

Every form field has a setting where you can set whether you want to show the field to only New Entrants, Known Entrants or Everyone. You will find this setting under "Advanced" in form field settings.