Thighten the M6 screw as its maximum. If the propeller can be removed, use a mallet and tap carrefully at the blade basis to unstick it. You can also introduce two screwdriver tips between the propeller and the generator, as a lever, but be carefull not to spoil the generator.
Insert the propeller on the shaft (2). Check that the stainless steel washer (12) is well set up. If not, do insert it. Insert the screw CHC M5x20 (21). Maintain the propeller with one hand and tighten the screw with a 4mm Allen key up until the screw drives the propeller.