Hello robin,
I’m indeed sorry to hear that…
To understand the function of release lever of the steering pin please take a look on the drawings of the patent M328409,
mentioned here: https://www.stridaforum.com/t/patent-documents-of-strida/600/1]
U.S version [url]http://www.freepatentsonline.com/7681900.pdf
(I mean you will just need the drawings.)
Or here: [url]How does the bottom bar latch work?]
I guess the latch (part 13) did stuck on the small pin (part 132), due to rust (?).
Maybe you can make it moveable again by using some oil.
If that does not work, you might consider to replace the complete Strida part.nr. 216 (steering pin).
(At least the Austrian Strida parts collectors do have it in stock 
)
Sorry, but I’ve got no valid info about Strida dealers near NYC, please ask Bill from Strida Canada West,
maybe he is able to help you:
http://stridacanada.ca/?page_id=110