Just having a room already booked does not mean you can apply a discount. It needs to be available for a new booking under the bounceback promo. If the resort or room type is sold out for new bookings, it’s highly doubtful they’ll apply the discount to an already booked room. Of course, someone will always come along & say a CM applied the discount for them anyway. Thats a very rare exception tho. So the only way to know for sure is to call & ask.