Ok I see the problem.
You see the giant pokeball in the room before you enter the chamber? You have to start there. From inside the pokeball take 6 steps down and 9 steps to the right. Then hit A. That should unlock Registeel.
Ok for the question about the sun. You would have to visit the chamber during the day. And then again at night to unlock Registeel. All it does it says what I just said above. One part will say 6 steps down and visit again during day/night. The other part will say 9 steps right and visit again during day/night.