snipe-it/app/Http/Controllers/Auth/RegisterController.php

<?php

namespace App\Http\Controllers\Auth;

use App\Http\Controllers\Controller;
use Illuminate\Foundation\Auth\ResetsPasswords;

class RegisterController extends Controller
{

    public function __construct()
    {
        $this->middleware('guest');
    }

    public function showRegistrationForm() {
        abort(404,'Page not found');
    }
    
    public function register() {
        abort(404,'Page not found');
    }
}