For each of your cores, you'll need to create a separate project in the IDE because each core will execute its own specific application. For handling multicore systems, the launch configuration lets you select a master project from the Master Launch field on the Trace32 Debugger tab.
Whenever the master project starts, the associated slave projects are also launched to ensure the correct start order. The type of a launch configuration (master vs slave) is indicated in the top left corner of the launch configuration dialogue.
For information about creating more complicated launch configuration and using Trace32Start, see the Lauterbach documentation included with the software.