How to remove when preload old ViewController on Swift?

I am loading and opening another WKWebView in advance to reduce loading time for other webpages in Main WKWebView.

But every time you open and close another webpage, the same page grows. When I close another webpage, I want to delete the closing webpage. What should I do?

Main.js

$(document).ready(function(){
var data = {
apiType : "preload",
parameter : encodeURI(`view/other?value="testvalue"`)
}
webkit.messageHandlers.TestApp.postMessage(data);
...








$('#openBtn').on('click', function(){
   var data = {
apiType : "openOther"
   }
webkit.messageHandlers.TestApp.postMessage(data);

MainWKWebViewController.swift

func userContentController(_ userContentController: WKUserContentController, didReceive message: WKScriptMessage) {
            case "preload":
                let parameter = message["parameter"] as! String
                preload(parameter)
                break
            case "openOther":
                openOtherScreen()
                break
...




func preload(_ prameter: String){
   let storyboard = UIStoryboard(name: "Main", bundle: nil)
   otherWebView = storyboard.instantiateViewController(withIdentifier: "OtherWebViewController") as? OtherWebViewController
   otherWebView.delegate = self
   otherWebView.paramFromMain = prameter
   otherWebView.loadViewIfNeeded()
   otherWebView.otherWebView.navigationDelegate = self
   preloadCheck = true
}
func openOtherScreen(){
  if preloadCheck {
      DispatchQueue.main.async {
          self.navigationController?.pushViewController(self.otherWebView, animated: true)
          self.preloadCheck = false
     }
   } else {
   }
}
...
extension MainWKWebViewController: OtherWKWebViewControllerDelegate {
    func HandleData(_ key: String){
        if  key == "reload" {
            self.mainWKWebView.reload()
        }
    }
}

OtherWKWebViewController.swift

case "Close":
     self.delegate?.HandleData("reload")
     self.navigationController?.popViewController(animated: true)
     break

Safari => Develop => TestIphone's WKwebViewList

https://ibb.co/BctV84B