You usually have 14 days in which to leave a review. However, it appears that due to a technical glitch neither party has been prompted to leave a review. If you are still within the 14 day period I would contact airbnb and ask them to send out their standard review request. This happened to me just once before and was quickly rectified, enabling both the guest and myself to leave our reviews. If you are past the 14 days you are probably too late but if it is an error on the side of airbnb perhaps they will make an acception. I don't know.