@Christos41
I assume this was/is one of your guests. All reservations are listed in "list of reservations" by guest name, button details (just hoovering over it shows reservationcode allready in the link) brings up the reservationcode and personal details. Also in Transaction History pages this information can be found, clicking the arrow next to the amount shows reservationscode. By downloading the CSV file and load it into a spreadsheet all details are on 1 row per reservation.
Hope this helps,
Emiel