Reconnect all 7 ribbon cables to the main PCB boards.

iFixit connector guide

Use extreme care while handling ribbon cables and connectors as they can be easy to damage.

Take the black tape from earlier, and slowly wrap it back around the main PCB assembly.

The rectangular plastic cover should lay in between the right most PCB board and the PCB board that hangs off of the assembly.

The tape should be wrapped tight enough so all of the ribbon cables are held out of the way of reinstalling the fixed barrel in the next step. However, avoid from wrapping it too tightly where it causes too much pressure on the PCB boards and other components.