Hi JL082!
If you check out our DIY articles we have many informational ones on the E92! In particular I found one for flushing the cooling system. If you scroll down to figure 8, you will find tips on using the bleeder screw to extract air from the cooling system.:
https://www.pelicanparts.com/BMW/techarticles/BMW-3-Series-E90/WATER-Draining_Filling_Cooling_System/WATER-Draining_Filling_Cooling_System.htm
Hope this helps!
-Matt