When a booking has been created, yet another guest needs to be added afterwards, it only takes a few steps to amend the booking.
In the booking page of the reservation go to the "Allocation section" and hit the More button:
Here you click on the pencil button (which means you can edit):
Now you click on the Pax button which is still grey:
Add all guests details and hit Save:
Although the Pax button is still grey, hit Save Changes in order to save the added extra guest:
You have now Successfully added another guest to the reservation: