Spectrum FT7 Coupler

[GRASHLEY]

I just received a Spectrum FT7 from repair (replacement unit).  It had not been properly packed, and arrived with the rear coupler knocked off.  It does not appear damaged, just loose.  I have no instruction sheet, and I have been unable to find a sufficiently detailed sheet to see how to reattach it.  It is not obvious how to remove the truck to get to the coupler box.  Can someone please help???

Gordon