Since it’s German, a Singer handcrank may work on it (the non-German 206 machines have an off-set motor-mounting boss and won’t accept a handcrank). I put a Singer handcrank on my German 216G machine, but it’s a 1960s machine, not a 1930s machine. Check to see if the boss (if it has a motor boss) is centered directly under the handwheel (you can tell by just eye-balling it).
If it was mine, I would put a spoked wheel on it and use it as a treadle, but that’s just me. Motors are for (should I dare say it?)........Woos.......people who don’t care terribly much for people-powered machines?.......
CD in Oklahoma