Reinvent the wheel
In the question: He found something that was well known.
(Modern Hebrew)
Translation
Expression (Hebrew)
הִמְצִיא מֵחָדָשׁ אֶת הַגַּלְגַּל
Definition (Hebrew)
בְּהַשְׁאָלָה: הִמְצִיא דָּבָר שֶׁכְּבָר יָדוּעַ.
(הָעִבְרִית הַחֲדָשָׁה)