To access to registrants management page, there are 3 different ways:
From this page, you will see list of payment records, filter payment records by Forms, by payment status, search for a payment record by First Name, Last Name, Email, Transaction ID....
On Payments management screen, you can press Export button in the toolbar to export payment records from one selected Form or from all Forms.
You can access to Payment Form -> Mass Mail to send emails to all users who made payment for a certain Form on your site