How do I fix a HTTP 404 error in my program

public class HomeController : Controller
{
    private testContext db = new testContext();
    List<Table1> thistable = new List<Table1>();
    [HttpPost]
    public ActionResult Index()
    {
        thistable = db.Data1.ToList();
        ...
        return View(thistable);
     }
}

@model IEnumerable<AllIndexTables.Models.Table1>
<h2>Index</h2>
<center>
    <table>
        @foreach (var item in Model)
        {
            <tr>
                <td>
                    @Html.TextBoxFor(modelItem => item.Idt)
                </td>
                <td>
                    @Html.TextBoxFor(modelItem => item.datetime0)
                </td>
                <td>
                    @Html.TextBoxFor(modelItem => item.col1)
                </td>
                <td>
                    @Html.TextBoxFor(modelItem => item.col2)
                </td>
                <td>
                    @Html.TextBoxFor(modelItem => item.col3)
                </td>
            </tr>
        }
    </table>
</center>