According to 2 Kings 22:8 "And Hilkiah the high priest said unto Shaphan the scribe, I have found the book of the law in the house of the LORD. And Hilkiah gave the book to Shaphan, and he read it." If Hilkiah found the Torah, Where were the books of Other prophets in that time?
The commentators refer this Sefer Torah to The Torah Moshe Rabenu wrote dictated by Hashem and that was the big celebration. More books of Torah were found among the Jews and same for the other Holy Scriptures.