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.
The Torx keys are made of high-quality chrome-vanadium-steel...
The adjustable gear lever for the BMW R1200GS and R1200GS...