How can I change US Visa appointment to interview Waiver (Dropbox)?

[getjig]

We have booked Visa appointment to renew Visitor (B2) visa for my parents in US Consulate of New Delhi, India, but we realized that they are eligible for Visa Interview Waiver Program. They are applying for same category and their visa is expired less than a year ago. Is there a way to change the application to cancel the visa appointment and apply through Interview Waiver Program. It looks like we can't go back to that option once we have paid the fees and booked appointment. Does any one know if it is possible? Or can I use the same fee receipt for different application submitted through different email address?