Laravel Tinker Not Working After Upgrading From 5.3 To 5.4

Edit your app/Console/Kernel.php, then modify the $commands property with this:

protected $commands = [
    //
    \Laravel\Tinker\Console\TinkerCommand::class,
];

then in console, make a

composer dump-autoload

Laravel Tinker

In order to continue using the tinker Artisan command, you should also install the laravel/tinker package:

composer require laravel/tinker

Once the package has been installed, you should add Laravel\Tinker\TinkerServiceProvider::class to the providers array in your config/app.php configuration file.

Source: https://laravel.com/docs/5.4/upgrade