If you’re looking for an explanation of the universe, which is a collection of contingent beings, there are only two possibilities: 1) The explanation is found in a necessary being that transcends the universe; 2) There is no explanation.
Regarding 1), every physical entity is a contingent being. The “universe” simply refers to the whole collection of physical, contingent beings. One cannot explain why the universe exists by appealing to another physical, contingent being because there can be no physical, contingent beings outside of the collection of all physical, contingent beings. “But,” one might say, “perhaps it could be explained by a prior non-physical, contingent being. Perhaps, but even if so, as a contingent being, that non-physical, contingent entity would also require an explanation for its existence. To avoid an infinite regress, one must ultimately arrive at a necessary being that transcends the universe, and explains why the universe exists.