How to insert more data when registering a user in Laravel Spark

I'm using Laravel Spark for my latest app and need to insert a random code to a column in the table upon registration.

After A LOT of digging through the code I've found this block of code:

/**
 * Handle a registration request for the application.
 *
 * @param  RegisterRequest  $request
 * @retu Response
 */
public function register(RegisterRequest $request)
{
    Auth::login($user = Spark::interact(
        Register::class, [$request]
    ));

    event(new UserRegistered($user));

    retu response()->json([
        'redirect' => $this->redirectPath()
    ]);
}

Which is found in LaravelSparkHttpControllersAuthRegisterController;

Which I assume is where the code for inserting a user into the database is happening. But I caot for the life of me work out how to populate a column called confirmation_code with something like 13sfet1201.

I'm so stuck on this, so please offer any advice you can.

Thanks in advance,

Andy