What should I do when I find a verse written in a way that contradicts my memorization of it? And is it obligatory for me to alert its writer, or to verify the correctness of its writing across all narrations?

If you find a discrepancy in a verse between your memorization and the Mushaf (copy of the Quran), then verify the source of the Mushaf and the riwayah (narration) by which it was written. If the riwayah is the same and the Mushaf is from a reliable source, the error might be in your memorization or from the printing press. Verify the error by consulting specialists or by comparing the Mushaf with other copies. If it becomes clear that the error is in the Mushaf, inform the relevant authorities and warn against this edition. If the Mushaf is according to a different riwayah than what you have memorized, it is most likely a difference in readings, so ask specialists. Do not recite except from a reliable Mushaf and according to the reading you have memorized.