First change the booking to reflect the correct number of nights - your guests will accept that at the higher rate.
Then you can send them a Special Offer, which should include the total costs agreed for the 4 nights accommodation, plus your cleaning fee. Do not add on the AirBnB service charges - that will happen automatically.
Once you send them the Special Offer they will need to accept it for it to be valid - so ensure that you get an acceptance email back to you and see it confirmed at the right rate in your reservations listings.