Hi there,
To incorporate extra charges for a guest stay, go online using a full laptop or desk top computer, then go to "reservations" > search through to see the reservation you want to deal with and you will see in red text, the message history and "alter or cancel"
Select "alteration" and proceed to enter the details to reflect the changes you wish to incorporate and charge for. Once you stop typing, it will automatically calculate new charges and you can send the request to your guest, who can then accept and approve the alteration during their stay. Your payout will be topped up if needs be.
To make a straight forward request for extra $ from your guest, you can do that via the "Resolutions centre", nominate the reservation and reason for requesting extra funds.
https://www.airbnb.com.au/help/article/50/can-i-change-a-reservation-as-a-host?topic=232
I hope this is helpful to you and others.
Sincere Regards
Christine.