JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://code.jquery.com/jquery-3.5.1.min.js" integrity="sha256-9/aliU8dGd2tb6OSsuzixeV4y/faTqgFtohetphbbj0=" crossorigin="anonymous"></script>

<!-- Latest compiled and minified CSS -->
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/3.4.1/css/bootstrap.min.css" integrity="sha384-HSMxcRTRxnN+Bdg0JdbxYKrThecOKuH5zCYotlSAcp1+c8xmyTe9GYg1l9a69psu" crossorigin="anonymous">

<!-- Optional theme -->
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/3.4.1/css/bootstrap-theme.min.css" integrity="sha384-6pzBo3FDv/PJ8r2KRkGHifhEocL+1X2rVCTTkUfGk7/0pbek5mMa1upzvWbrUbOZ" crossorigin="anonymous">

<!-- Latest compiled and minified JavaScript -->
<script src="https://stackpath.bootstrapcdn.com/bootstrap/3.4.1/js/bootstrap.min.js" integrity="sha384-aJ21OjlMXNL5UyIl/XNwTMqvzeRMZH2w8c5cRVpzpU8Y5bApTppSuUkhZXN0VxHd" crossorigin="anonymous"></script>

<form method="post" action="promocodes/update" id="editForm" role="form" data-toggle="validator">
    <div class="modal-body">
        <div class="container">
            <div class="row">
                <div class="col-md-12 mb-4 edit_valuePromocode">
                    <label for="edit_value">Что даёт промокод</label>
                    <select name="value[]" class="form-control d-none" id="edit_nomenclature" multiple="">
                        <option value="2b2df5f4-256d-402e-b074-c460ee394a2e">Салат Калифорния</option>
                        <option value="fd199543-3f09-470d-9554-8c888bfaa3f7">Салат с угрем</option>
                        <option value="a81e8399-3d09-403f-83ee-ef00d93d000b">Чука с угрем</option>
                        <option value="c60e9c71-bc97-47f7-a72f-cae363739d8a">Дзо Cуй</option>
                        <option value="f24f8de3-b37b-4dac-90c5-5596505963b4">Куросама</option>
                        <option value="9aeb2ea2-798c-45dd-8c91-a8d34704663c">Мисо суп</option>
                        <option...

JavaScript

$(document).ready(function() {
        var data = {"value":"[\"2b2df5f4-256d-402e-b074-c460ee394a2e\",\"a81e8399-3d09-403f-83ee-ef00d93d000b\"]","days":"[\"\\u041f\\u043e\\u043d\\u0435\\u0434\\u0435\\u043b\\u044c\\u043d\\u0438\\u043a\",\"\\u0412\\u0442\\u043e\\u0440\\u043d\\u0438\\u043a\",\"\\u0421\\u0440\\u0435\\u0434\\u0430\"]"};

        //var json = JSON.parse(data);
        var json = JSON.parse(JSON.stringify(data));
        console.log(json);

        $('#edit_nomenclature').val(json.value);
        $('#edit_days').val(json.days);
    });