So whomever you bought the car from had a leaking coolant flange, the 3 outlets from the firewall. So they just bypassed the heating system/core all together. First you need a new flange.
#11
http://www.realoem.com/bmw/enUS/show...diagId=64_0555 Part# 64118390697 -
https://www.ecstuning.com/b-genuine-...e/64118390697/ Then it's a matter of reconnecting, checking for leaks and adding coolant.