First of all Override the following file :

/vendor/magento/module-customer/Model/Account/Redirect.php

• change redirect URL if login post controller gets 404 error or redirect the customer to a specific page :

  private function applyRedirect($url)
  {
     /* changes start*/
      $baseUrl = $this->storeManager->getStore()->getBaseUrl();
      if($url == $baseUrl.'customer/account/loginPost/'){
          $url = $baseUrl.'customer/account/login/';
      }
     /* changes  end*/
      $this->session->setBeforeAuthUrl($url);
  }

  NOTE:  Override core file in your custom module.