Resizing of cameraOverlayView in UIImagePickerController

I’m developing a Camera App (with Xcode 12.2 & Swift 5.3.1.) by using UIImagepickerController.   

In the Camera App, I want to put a semitransparent-image (image previously captured and make it semitransparent then overlaying) on the camera view (real-time view).  

Now I can put a semitransparent-image on the camera view as shown in those figures, however the size of the semitransparent-image is not suitable. 
The size of the semitransparent-image is too big (Figure 4 in the following link) than that of I want to display (Figure 3).

https://imgur.com/eUnBQzd

Could you tell me way to change (fit) the size of the semitransparent-image?In concretely, I want to change the size of image that displayed by “UIImageView(image:UIImage(named: “default”))” in the following source codes.

Code Block language
import UIKit
class ViewController: UIViewController ,UIImagePickerControllerDelegate ,UINavigationControllerDelegate{
  @IBOutlet weak var previewView :UIImageView!
  let overlayView = UIImageView(image:UIImage(named: "default"))
   
  @IBAction func startCmamera (_sender : UIBarButtonItem) {
     
    if UIImagePickerController.isSourceTypeAvailable(UIImagePickerController.SourceType.camera){
      let picker = UIImagePickerController()
    picker.sourceType = .camera
      picker.delegate = self
      overlayView.alpha = 0.4
      picker.cameraOverlayView = overlayView
      self.present(picker, animated: true)
       
    }
  }
   
  func imagePickerController(_ picker: UIImagePickerController,
                  didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any]) {
   let image = info[UIImagePickerController.InfoKey.originalImage] as! UIImage
    previewView.contentMode = .scaleAspectFit
    previewView.image = image
    UIImageWriteToSavedPhotosAlbum(image, nil, nil, nil)
     
    self.dismiss(animated: true)
     
    }
   
   
  override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view.
  }
}