Jesus did not pre-exist his birth
God is the author of our existence. We live in the book he has already written that we are living out. So when God has a plan or thought, it will come to pass. Many creations, plans and glories have already been stored, awaiting the right time for those worthy to receive it before the foundation of the world was even created. For example, talking about Jesus……
(1 Peter 1:20) 20 "He was known before the foundation of the world, but was revealed in the last times for your sake."
(1 Corinthians 15:45-47) 45 So it is written: “The first man Adam became a living being”; the last Adam a life-giving spirit. 46 The spiritual, however, was not first, but the natural, and then the spiritual. 47 The first man was of the dust of the earth, the second man of heaven. This firmly explains, that the first man was adam, and the spiritual man was second. The first man was of dust, the second of heaven.