This setting is provided for each of the event at the event level.
Please go to Event Setup/See more features
Click Settings Cards and Select Other Settings
Once this is enabled, the Checkout page would change automatically. It will ask the Member to enter the email id and Password.
Basis the entered data, system will authentic the person and show the relevant tickets and also it will load the data in the attendee form.
This particular feature should be used only when a chapter is very sure that this event is only for Members of the chapter irrespective of membership type.