We have been out for the evening so I am playing catch up now. I can’t remember which engine I was working on but it wasn’t the blue one.
I am trying to remember exactly what I did to move the worm down the shaft and I believe what I did was to put a flat bladed screwdriver on the underside of the laminations which has a black plastic insulator and wedge it against the chassis and lever up the armature which effectively shifts the worm gear down the armature shaft. Just be mind full that you don’t have to move it much and check for alignment after each small movement.
These are really cheap and cheerful engines and the engineering for them is pretty poor.
