This largely revolves around filtering on the Bookings page, and how you've set up the group booking. You'll need one of these things to do it:
All of the bookings with the same booking ID (in the form of a group booking)
All of bookings have the same agent (like if it's a corporate booking).
Searching by booking ID:
You'll need to know the booking ID for your reservation first. When you click on the booking, on the summary page is the booking ID.
Jump onto the Bookings page from the navigation bar in Preno.
Enter the booking ID into the search bar. Preno will filter through your bookings to find that reservation, and then you can press Print.