If you need to disassemble the rotor This operation requires quite a bit of strength. Disassemble the rotor with a rocking motion as if trying to break it and at the same time pulling the ends out. In the starting position the light from the LED reaches the phototransistor because the disk blade is not in the optointerrupter slot. Make sure that in the starting position one of the blades is inside the optointerrupter slot and does not allow light from the LED to reach the phototransistor. While holding the magnets, slightly rotate the cap with the disk to find the proper disk blade position.
Rotor is jammed.
Find the exact cause and fix the problem. This may require breaking off the stands and reattaching them to the board. You may try to lubricate the axles with WD-40 or any other lubricant. Electromagnet attracts the magnets instead of repelling them. Switch the electromagnet wires.