In The Name of Allah, The Ever Merciful, The Most Merciful.
Where are the previous divinely-revealed Books?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

If you mean by the previous divinely-revealed books: the Torah, the Gospels, the Psalms, and the Scriptures of Ibrahim (Abraham), it should be known that these books were distorted by addition and deletion and some of them are totally lost, and the remaining parts are mixed with distorted texts. They are available in the hands of those who follow the distorted forms of Christianity and Judaism.

Now, there is no divinely-revealed Book safe from corruption and distortion but the Noble Quran, of which Allah Took it upon Himself to guard it and did not entrust this task to humans. Allah The Almighty Says (what means): {Indeed, it is We who sent down the Quran and indeed, We will be its guardian.} [Quran 15:9]

That is because the Quran is the last revealed Book to the last Prophet. So, it must be preserved to remain a proof among people and a miracle for the last Prophet.

Allah Knows best.