There is a drilling in the side of the plug in which you can put a size 3 Allen key or a Torx key T10 (usually found in the your BMW toolkit) in order to fit and remove it.
See tools
Also referred to as oil filler cap.
Oil filler plug Torx, made of high-quality aluminium....
These covers for the open holes beyond the seat are made of...
Cover for the foot brake fluid reservoir, CNC machined of...