You can't find it, because you never lost it. You can only give up the finding and the you (the finder). Then, there's only it left. That's all. That's it. So, let yourself dissipate and unbecome. Let yourself die.
What is it? It is the void whence everything springs, the emptiness behind all, nothing yet everything. It is formless, yet all forms are it. It is the unknown, yet you can't speak of or talk about it, for words are too incapable. It is the doer, the doing, and the object of the doing at the same time: the subject, the verb, and the object simultaneously. How are you supposed to say such a thing? The unknown unknows the unknown? Or ??? ?
I can't tell you what it is. I can definitely tell you what it is not. It is nothing you know and think of because knower-knowing and thinker-thinking are both illusionary dualities.