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.
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Also referred to as oil filler cap.
The Torx keys are made of high-quality chrome-vanadium-steel...
Made of 3 mm aluminium with the latest laser-cutting and...
The joint is the mount / adapter for the footrest...