@Susan4642
The only way to do this is if the guest cancels (don't cancel yourself as you will face penalties) or you agree to change the dates.
Are you giving the guest a refund for the unspent nights? If not, there's really no incentive for them to cancel. If you do plan on giving them some sort of refund, then that's a different matter. You can either offer them the refund if they cancel or, what I would do is suggest that you will refund them if you are able to rebook the dates, but you can only do that if they cancel, so the sooner they do that the better. Just be clear that there is no guarantee that the dates will be rebooked and you can only refund them for dates that are.