Now, gently and carefully put the amp assembly back down onto your work surface. Notice the green PCB (circuit board) there. That's the PCB for the speaker terminals, surrounded on one side by some foam insulation to prevent air leakage.

Gently pull the green PCB up and out of the opening in the amp wall by pulling from the sides of the black foam around the edge. DON'T pull or strain any of the coloured wires attached.