Brother took down their vintage manuals years ago. There's no longer anyone working for Brother who knows spit about vintage machines. I have the manual on my desktop which is currently in storage but I know somewhere you can find it for free. If you're on Facebook it's in the files of the Vintage Sewing Machines (Non Singer) group.
To get the machine out of zig zag you just loosen the stops(the 2 little silver knobs) and set the stitch width to the left of them to zero. You should also be aware that this is a left homing machine so the needle will always be in left position, not in center position for straight stitching.
Cari