Get Default Value for DropDownListFor from database

-1

I coded a website to collect student information including 3 dropdown lists: Province, District, Ward. When I create a new student, I get the Province, District, Ward data from the database to enter each DropDownListFor very well, but when I go to the function of editing student information, I don't know how to get the data from the previously saved database to enter each DropDownListFor.

I use ASP.NET Core MVC and Html Helper to do it. I hope you can guide me.

Here is my code

    <div class="col-md-2">
        <label for="MATINH">Province</label>
        @if (ViewBag.TINH != null)
        {
            @Html.DropDownListFor(m => m.MATINH, ViewBag.TINH as SelectList, "---Select---", new { @class = "form-control" })
        }
    </div>
    <div class="col-md-2">
        <label for="MAHUYEN">District</label>
        @Html.DropDownListFor(m => m.MAHUYEN, new SelectList(""), "---Select---", new { @class = "form-control" })
        <script src="~/Scripts/jquery-3.4.1.min.js"></script>
        <script>
            $(document).ready(function () {
                $("#MATINH").change(function () {
                    var matinh = $(this).val();
                    debugger
                    $.ajax({
                        type: "post",
                        url: "/Giaovien/LayHuyen/" + matinh,
                        contentType: "html",
                        success: function (response) {
                            debugger
                            $("#MAHUYEN").empty();
                            $("#MAHUYEN").append(response);
                        }
                    })
                })
            })
        </script>
    </div>
    <div class="col-md-2">
        <label for="MAXA">Ward</label>
        @Html.DropDownListFor(m => m.MAXA, new SelectList(""), "---Seleect---", new { @class = "form-control" })
        <script src="~/Scripts/jquery-3.4.1.min.js"></script>
        <script>
            $(document).ready(function () {
                $("#MAHUYEN").change(function () {
                    var mahuyen = $(this).val();
                    debugger
                    $.ajax({
                        type: "post",
                        url: "/Giaovien/LayXa/" + mahuyen,
                        contentType: "html",
                        success: function (response) {
                            debugger
                            $("#MAXA").empty();
                            $("#MAXA").append(response);
                        }
                    })
                })
            })
        </script>
    </div>
</div>