Try to get through to human interaction in the webchat; there is no doubt that you will and should be able to rebook, i.e. no change fee applicable or fare increase.

But you really need to consider your options now because in reality you have ticket valid (at least) +/- 14 days to any flight within the FR network, i.e. such a cancellation can be worth a lot. During covid I have rebooked several cheap tickets to Poland for flights to Spain where the fares had gone through the roof. So depending on how much you paid for the existing ticket, how much a ticket for the new flight would cost and if you are can make use of a "free" ticket, there are other options that just confirming or getting moved to the flight that you refer to.