Hi Alok,
Thanks for reaching out! Unfortunately, there’s currently no way to make a group of RSVPs or tickets become available after another type has sold out. However, you can achieve this effect by manually editing your event. Simply edit the event to add a waiting list RSVP type once your main RSVP type is out of stock. Your original RSVP type will remain at its existing stock level, and you can set the stock amount to whatever you’d like for your waiting list. 🙂
I hope that helps to get you started here! Thanks again, and let us know if you should have any other questions!