Heals,
According to the parts diagram it’s a 4mm dowel pin (probably a roll pin, or spring pin depending on where you grew up).
Use a punch, a dowel punch not a nail punch, 4mm ideal 1/8″ or a 3mm if not.
If you don’t have a punch grind flat the point of a nail 4mm or slightly smaller. Their not as strong but if you hit nice and square you shouldn’t bend the nail. Their cheap anyways.
Support the underside of the shaft opposite to where your hitting to avoid stressing the shaft or bushing for the shaft. Make sure you don’t block the dowel though. Don’t laugh I’ve seen it happen.
Hope this helps 
Adam.