To assign flights to crew members the Roster Gantt needs to be open and one half set to display legs / pairings and the other half to display crews. Displays can be chosen from the Gantt View Dropdown at the left end of the menu bars in the Roster Gantt.
Mark the flights to be assigned.
You mark a flight either by activate the Select symbol
or by hold the Ctrl key and click on the leg.
Left click on a selected leg and drag down to the crew member.
Repeat as needed until the flights are fully covered.
Please note that the process if the same for legs and pairings.
If you don't like drac and drop you use the user preference setting "GanttAssignOnClick" this will change the assign method to Mark and Click