The Nāsadīya Sūkta (after the incipit ná ásat, or "not the non-existent"), also known as the Hymn of Creation, is the 129th hymn of the 10th mandala of the Rigveda (10:129).
Brereton and Jamison in their translation to this hymn, say as follows:
This is one of the most famous hymns of the R̥ig veda, and one of the
most significant for later Indian cosmogonies. Because it is elusive
and suggestive rather than directly narrative, it has given rise to a
wide variety of interpretations.
Though subsequent literature like brAhmanas, puranas, etc, tried to explain the process of creation, after deification of Gods took place, attributing either to prajApati, or brahma or Shakti, etc, it is the Rig Veda, which is the source for every type writings in subsequent literature.
The answer is clear from the Hymn, as mentioned in the last mantra.
He who is the Eye above, in the highest space. He surely knows.
….. or if he doesn’t know
The composer of this hymn is a seer or drastha. We have to accept the seer's conclusion that only the CREATOR knows how the creation came into existence.