if you already accepted the reservation you always can go to the resolution center and ask for the extra payment explaining the problem, you could sound a little rude but it's 50%-50% chance they will accept... If you did not accepted you can decline the booking and change the price... or decline and send a "special offer" to your guest with the correct price... But settings, including prices, are part of the many glitches on Airbnb... Most likely this is one of them... When I change my prices check and double check to make sure it worked...