this is what you’d need to do. My experience is that just canceling, then rebooking will leave the same fare option on the same flight as ‘not available’. So easiest way to do this is to change to a different flight same day, next day, etc, then change back. IME, also easiest to make sure the flight you change to either has the same fare you originally bought for, or same as the new fare, as it simplifies the process a bit - you won’t need to spend more out of pocket and you’ll get one FFC (per person) for Whichever change has the difference.