How to change UICollectionView Scroll Direction?

This is how you create it in code with UICollectionViewFlowLayout

let layout = UICollectionViewFlowLayout()
layout.scrollDirection = .vertical
let collectionView = UICollectionView(frame: frame, collectionViewLayout: layout)

or if you are working with an existent collection view

if let layout = collectionView.collectionViewLayout as? UICollectionViewFlowLayout {
    layout.scrollDirection = .vertical
}