I haven't had a problem like that, but have read that perhaps there is some dried oil somewhere holding it in reverse. I think the lever above the stitch length knob is for temporary reverse. The knob has red numbers and black numbers. The red numbers are for prolonged sewing in reverse.
I would take the top off (if possible - it looks like you could) and move the lever and/or the knob and see if either is stuck. Some of the European machines have 'tricks' to get the top off and some are just a couple of screws.
Maybe post in the Vintage forum?
Janey - Neat people never make the exciting discoveries I do.