What is the ruling regarding someone who has prayed for years facing the wrong direction, then discovers the correct direction of the Qiblah, and how can the direction of the Qiblah be determined in Egypt?

The person mentioned erred in not taking precautions regarding the direction of the Qibla. Therefore, if his deviation from the Qibla does not reach the extent of invalidating the prayer, he is not required to repeat it. He must strive to determine the direction of the Qibla, and he can use the mihrabs (prayer niches) of Muslims as a guide, or rely on information from trustworthy individuals among them, or use astronomical signs. For example, for someone in Egypt, they can position the North Star (celestial pole) opposite their left ear and then face East.