Pass (Send) Html.DropDownList selected value from View To Controller in ASP.Net MVC

Hi,

I have a dropdown list for my report to choose an option and based on the option i will generate the code that. clicking the submit button is not doing anything.

index.cshtml

<label class="from-label">Reports</label>
<hr />
@Html.DropDownList("options",
    ViewBag.options,
    "Select an option",
    new {@class="form-control"})

and this is the controller (now it is only for 7 days just testing why its not fired when the button is clicked):

public async Task<ActionResult> Index()
{

    //Last 7 days
    DateTime StartDate = DateTime.Today.AddDays(-6);
    DateTime EndDate = DateTime.Today;

    List<Transaction> SelectedTransactions = await _context.Transaction
        .Include(x => x.Category)
        .Where(y => y.Date >= StartDate && y.Date <= EndDate)
        .ToListAsync();

    // total income
    int TotalIncome = SelectedTransactions
        .Where(i => i.Category.Type == "Income")
        .Sum(j => j.Amount);
    ViewBag.TotalIncome = TotalIncome.ToString("C0");

    // total expense
    int TotalExpense = SelectedTransactions
        .Where(i => i.Category.Type == "Expense")
        .Sum(j => j.Amount);
    ViewBag.TotalExpense = TotalExpense.ToString("C0");

    // Balance
    int Balance = TotalIncome - TotalExpense;
    CultureInfo culture = CultureInfo.CreateSpecificCulture("ae-AE");
    culture.NumberFormat.CurrencyNegativePattern = 1;
    ViewBag.Balance = String.Format(culture, "{0:C0}", Balance);


    return View();
}

how to take the choosen option (for example "Last 7 days" into the controller page and use it in an if statement: