Once you <enable and assign your crew roles>, you can assign those roles to crew members on the Dispatch Schedule by slot.
Go to Dispatch and click the Scheduling tab.
Click Crew Members.
Click the crew member's name from the list and drag them over to the slot. They are automatically assigned to the role that's set as their default.
To assign a crew member to a role different than their default, just drag them into the desired role.
Note: New temporary crew members will have all enabled role options available.