The pedal and cord are probably just missing. You need replacements. Don't bother about treadling a 401 unless it came as it originally. There are plenty of original trealde setups ot there if you need one.
LOL. Janey (or John), I have to say, I know what a treadle is, but I would just describe it as a sort of manually pedalling the machine in stead of motor ;- ) Not ideal words chosen for an official manual, but...