Nodemcu can't reconnect when the wifi router turns off and turns on again

When the power is off and back on again, the wifi router and nodemcu will turn on at the same time but the wifi router will take at least 30 seconds to normalize but nodemcu can’t reconnect when the wifi router turns off and turns on again.
nodemcu have to wait for the wifi router to turn on normally again to connect … how to solve it if we were out of town? Thank You

Note : I am using a nodemcu based module with a mains charger adapter ( am also using Wifi manager to sync wifi to setup before)

What is your code doing after a reboot ? Will it constantly try to connect to the wifi or reset the ESP ? Without seeing the code its hard to say. If you are using the new BlynkIoT then you need not have wifi manager.

Post your code here properly formatted.
add triple backticks at the beginning and end of your code so that it displays correctly. Triple backticks look like this: ```

Try this.

  Download latest Blynk library here:
  Blynk is a platform with iOS and Android apps to control
  Arduino, Raspberry Pi and the likes over the Internet.
  You can easily build graphic interfaces for all your
  projects by simply dragging and dropping widgets.
    Downloads, docs, tutorials:
    Sketch generator: 
    Blynk community:  
    Follow us:        
  Blynk library is licensed under MIT license
  This example code is in public domain.
  This example shows how to keep WiFi connection on ESP8266.

/* Comment this out to disable prints and save space */
#define BLYNK_PRINT Serial

/* Fill-in your Template ID (only if using Blynk.Cloud) */
//#define BLYNK_TEMPLATE_ID   "YourTemplateID"

#include <ESP8266WiFi.h>
#include <BlynkSimpleEsp8266.h>

// You should get Auth Token in the Blynk App.
// Go to the Project Settings (nut icon).
char auth[] = "YourAuthToken";

// Your WiFi credentials.
// Set password to "" for open networks.
char ssid[] = "YourNetworkName";
char pass[] = "YourPassword";

int lastConnectionAttempt = millis();
int connectionDelay = 5000; // try to reconnect every 5 seconds

void setup()
  // Debug console

  Blynk.begin(auth, ssid, pass);

void loop()
  // check WiFi connection:
  if (WiFi.status() != WL_CONNECTED)
    // (optional) "offline" part of code

    // check delay:
    if (millis() - lastConnectionAttempt >= connectionDelay)
      lastConnectionAttempt = millis();

      // attempt to connect to Wifi network:
      if (pass && strlen(pass))
        WiFi.begin((char*)ssid, (char*)pass);

If he is on the new Blynk Edgent example, the reconnection part already exists in the code. And it does connect when the wifi is back.

He has not shared enough information.