Navigation1: 'Order' form → 'Manual Segments': 'New PNR' button
Note
To delete existing relation select it at 'Flight Relations' tab in 'Relations' section and push 'Remove' button.
Manual flight booking can be also created by convertion from automatic one:
Navigation2: 'Order' form → open existing flight segment → check 'Manual' checkbox in the upper right corner of the segment form.