How did Joseph's father become a seer once again?

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By having Joseph's shirt laid upon his face

Go with this shirt of mine and lay it on my father's face, he will become (again) a seer....

When the caravan departed their father had said: Truly I am conscious of the breath of Joseph, though ye call me dotard.

... He laid it on his face and he became a seer once more. Quran 12:93-95