iam just finninshing of my rebuild and when i cam to fit my heat exchangers there seems to be a peice missing or iam going mad

i have all the pipes but there is a square outlet at the side of the exhaust bracket what the hell fits there or should it be open? ive rang round no one can help vw herritage sent me the part they think it may be but it was only a small plate that bolts onto the exchanger but still leaves a hole

its for warm air but should it go to somthing ?