As noted by the philosopher (atheist) Daniel Hume, this is an old and unfounded argument that a philosophy student with good talent can refute. For an explanation to be successful, there is no need for an explanatory answer. When we see the complexity of the world, we are asked to offer the existence of GOD as an explanation for that complexity, and this is indeed a successful explanation. Even if the question arises as to the explanation for the existence of GOD himself, it does not at all detract from the evidence for his existence. For example, why is this similar?
Suppose there is some complex device on Mars. When we look for an explanation for the existence of the device, we conclude that the most successful explanation is that intelligent aliens created it. The existence of the device therefore constitutes evidence for the existence of intelligent aliens.
The fact that we do not know who designed the aliens themselves does not usurp our explanation for the design of the device and the aliens’ existence. An explanation can be successful and satisfying, even if it is impossible to find out the whole chain of reasons that led to it. Had it not been so, the entire Big Bang theory would have been refuted as an explanation for the cosmic background radiation. For it is not known what caused the big bang itself, and even the theory of evolution was refuted because it does not explain the appearance of the first cells.
In other words, an explanation can be successful even if it does not explain everything. When we ask ourselves who created the complex universe, the most successful explanation for it is GOD, and even if we do not know how to explain GOD himself, it is irrelevant.