R56 N12 oil separator cover

Hello guys,
I have some small problems with my mini cooper r56 n12 (non turbo) engine, RPM falls when puting neutral, after it gets hot it occasional go flat and I have to start it again. It all started after changing oil and air filter. Last weekend I checked with obd that it shows air sensor error.
I cleaned up throttle, it was covered slightly in oil. Now I wanted to check how the oil separator looks inside, but I have no idea how to open the cover.
I found the new replacement, tho I preffer not to waste money if I can just clean in it.

Anyone ever popped open this cover?



inside looks like this

Thanks in advance.