Unscrew the plastic ring, turn rubber ring, plastic ring screws and fix it again. Hmm, is not still. Ok, again screwed and ... oops, can these small plastic adapter turn behind the rubber ring also? Times tried and lo and behold, now it fits. Quite comfortable inflating runs but then not because you have to aufbringen- "back pressure" with your hand and hold the pump already quite a good, otherwise the air escapes again.
Otherwise, the part looks good and is really very small and handy. The double-stroke function reduces the inflation considerably. So all in all ok ... if you get the hang times. Professionals goes the whole may be easier on the hand.