DÜRKOPP ADLER 219, presser foot is locked, help!

[Akse]

I own a DÜRKOPP ADLER 219 with air-operated lifting of the presser foot. When lubricating the sewing machine, I used my fingers to manipulate the mechanical parts inside the machine. When I manipulated the presser foot mechanism, the foot lifted and there was a clicking sound, similar to what you would expect when activating a locking mechanism. The foot is locked in upper position. However, I am unable to figure out where and how to release the foot lift mechanism again. Please advise.