How can I free cutter knife from Bamix Stick blender?

Bamix blender cutter/knife is stuck to shaft and cannot be removed for cleaning ,.we immersed it in boiling water and
let the Bamix swirl for some time but could not get the cutter free. .
the cutter is held in place by a small pin but we cannot
move it nor free the cutter as there is no space to hold
and stop the shaft from rotating .