SceneDelegateDidAdd.swift

func renderer(_ renderer: SCNSceneRenderer, didAdd node: SCNNode, for anchor: ARAnchor) {
  //Check that anchor is plane anchor that represents planar surfaces
  guard let planeAnchor = anchor as? ARPlaneAnchor else { return }
  //Create node using anchor position
  let boxNode = createNode(with: planeAnchor)
  //Add boxNode as a child node to newly found node
  node.addChildNode(boxNode)
}

func createNode(with anchor: ARPlaneAnchor) -> SCNNode{
   let boxGeometry = SCNBox(width: 0.2, height: 0.2, length: 0.2, chamferRadius: 0)
   let node = SCNNode(geometry: boxGeometry)
   node.positon = SCNVector3(anchor.center.x, anchor.center.y, anchor.center.z)
   return node
}