Its not a bolt, its a fluid level sensor, essentially a bobber on a stick. Note the orientation of the point on the black part in the middle of the white nut. It needs to be put back in the same orientation it is removed, typically 6 o'clock. You also need to put a wrench on this to prevent it from turning as you loosen the white nut. Once the nut is loosened and pulled out to the connector on the wires, DON'T remove it from the wires. Its a pain to put back on. Don't remove the rubber grommet either. You should now be able to remove the bobber from the tank. Add sufficient Dexron III to to fill the reservoir up to the edge of the hole. Replace sensor with point in 6 o'clock position.