В Быстром

var collectionView: UICollectionView!
let layout = UICollectionViewFlowLayout()
collectionView = UICollectionView(frame: .zero, collectionViewLayout: layout)
layout.scrollDirection = .vertical
view.addSubview(collectionView)

Swift 3.0, Swift 4.0 и Swift 5.0

Это - работа для меня.

let collectionView = UICollectionView(frame: CGRect.zero, collectionViewLayout: UICollectionViewFlowLayout.init())

В Методе (внутри viewDidLoad)

if let flowLayout = collectionView.collectionViewLayout as? UICollectionViewFlowLayout {
    flowLayout.scrollDirection = .horizontal
}