How to reply a letter in laravel?

i'm using Laravel 7 to make a automation system. i have a letter, i can send it to one or many recievers. after that i have to be able to send reply to that letter, it's a loop and can be reply several times. This is my letter table structure : Letter Table Structure

as you can see i have a replyto field

i don't know how can i make this controllers or also table fields

here is Store function for Letter :

public function store(Request $request)
{
    $recieve_ids = $request->recieve_id;
    foreach ($recieve_ids as $recieve_id) {
        Letter::create([
            'indicator_id' => $request['indicator_id'],
            'sender_id' => auth()->user()->id,
            'recieve_id' => $recieve_id,
            'title' => $request['title'],
            'image' => 'default.png',
            'description' => $request['description'],
            'date' => $request['date'],
            'text' => $request['text'],
            'number' => '100',
            'refrence_text' => ' ',
            'replyto' => 0,
        ]);
    }
    return redirect(route('Letter.index'));
}

and this is my reply_letter function for show reply page, but i don't know how can i insert new data (new reply) to letter :

public function reply_letter($id)
{
    $v = new Verta();
    $date = $v->format('%d %B %Y');
    $letter = Letter::find($id);
    return view('Letter.reply', compact('date', 'letter'));
}

reply can be done by sender or reciever letter.

Thank you for your help <3

via Chebli Mohamed