Add refresh button to error page - Webview

Question

I created a simple web page and added an error page if there is any error, for example, there is no internet connection. And it successfully loads the error page when there is no network. My problem is that I cannot add an update button to the html resource page. How to add refresh button to your html resource. when I click the refresh button, it should reload the last web browser URL. Please help me Devs! Here are my codes

Webview.java

public class WebView extends Activity  {
   Button b1;
   EditText ed1;

   private WebView wv1;
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);

      b1=(Button)findViewById(R.id.button);
      ed1=(EditText)findViewById(R.id.editText);

      wv1=(WebView)findViewById(R.id.webView);
      wv1.setWebViewClient(new MyBrowser());

      b1.setOnClickListener(new View.OnClickListener() {
         @Override
         public void onClick(View v) {
            String url = ed1.getText().toString();

            wv1.getSettings().setLoadsImagesAutomatically(true);
            wv1.getSettings().setJavaScriptEnabled(true);
            wv1.setScrollBarStyle(View.SCROLLBARS_INSIDE_OVERLAY);
            wv1.loadUrl(url);
         }
      });
   }

   private class MyBrowser extends WebViewClient {
      @Override
      public boolean shouldOverrideUrlLoading(WebView view, String url) {
         view.loadUrl(url);

      public void onReceivedError(WebView view, int errorCode, String description, String failingUrl) {
        myWebView.loadUrl("file:///android_asset/my_custom_err_page.html"); //My Error page
           }
         return true;
      }
   }

Thanks at Advance!