Do this...
Add this to your User model...
use App\Notifications\ResetPasswordNotification; // At the top under your namespace
public function sendPasswordResetNotification($token)
{
$this->notify(new ResetPasswordNotification($token));
}
Note: You're doing this to override User > Authenticable > CanResetPassword > sendPasswordResetNotification
Create a new notification...
php artisan make:notification ResetPasswordNotification
Open app/Notifications/ResetPasswordNotification.php
There you can modify your email. If you want to copy off the original, look in vendor/laravel/framework/src/Illuminate/Auth/Notifications/ResetPassword.php.
Do NOT modify "core" aka vendor folder code to do this. Everything can be extracted to your app folder. What this article is suggesting to do is a rookie mistake.