What should one do if he became impure, then realized the impurity after some time? Should he search for the places that became impure because of him to purify them, and what should he do if he cannot identify those places?

If one knows that there is impurity on his garment, he must remove the garment or wash it. Impurity must be removed from the body and garment. As for other clothes and places to which impurity might have transferred due to their dampness, if he knows about them, he must purify them if he intends to pray in them or on them. If he does not know about them, then there is nothing upon him, because the default state of things is purity.