Click the drop-down menu that will allow you to define the location of the master...

Click the drop-down menu next to"Interconnect bay set".

To define the location of the master modules within the logical interconnect group, you need to select the appropriate interconnect bay set. The drop-down menu next to "Interconnect bay set" allows you to specify which bays the interconnect modules will be placed in, thereby determining the location of the master modules.