Inventory: update stock according to the amount that the user enters in an input in razor

I'm doing an inventory system, where I have to add or remove stocks of a product. I currently have a table producto where I keep the product data (as well as the amount that I have in stock), and a table movimientoEntrada , where I record an entry, the product that enters and the amount of that product that comes through of a TextBox.

I am using entity framework to make the connection to the base and use scaffolding to make some interfaces, the problem is that I can not find a way to add the amount of product that enters specified in the input of the view of movimientoEntrada , or failing to add the values of the tables to be able to update the stock that I have, these are my codes:

Class / Table movement Entry:

public class MovimientoEntrada
{
    public int Id { get; set; }

    public int ProductosId { get; set; }
    [ForeignKey("ProductosId")]
    public virtual Productos Producto { get; set; }
    public List<Productos> ProductoCollection { get; set; }

    public int Cantidad { get; set; }
}

class / table Products:

public class Productos
{
    public int Id { get; set; }
    public int CodigoBarras { get; set; }
    public string Nombre { get; set; }
    public int Precio { get; set; }
    public int Cantidad { get; set; }
}

Code in controller with which I generate a new movimientoEntrada :

    [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult Create([Bind(Include = "Id,ProductosId,Cantidad")] MovimientoEntrada movimientoEntrada)
    {
        if (ModelState.IsValid)
        {
            db.MovimientoEntradas.Add(movimientoEntrada);
            db.SaveChanges();
            return RedirectToAction("Index");
        }
        ViewBag.ProductosId = new SelectList(db.Productos, "Id", "Nombre",  movimientoEntrada.ProductosId);
        return View(movimientoEntrada);
    }

My view code of movimientoEntrada :

@using (Html.BeginForm())
{
    @Html.AntiForgeryToken()

    <div class="form-horizontal">
        <h4>MovimientoEntrada</h4>
        <hr />
        @Html.ValidationSummary(true, "", new { @class = "text-danger" })
        <div class="form-group">
            @Html.LabelFor(model => model.ProductosId, "ProductosId", htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.DropDownList("ProductosId", null, htmlAttributes: new { @class = "form-control" })
                @Html.ValidationMessageFor(model => model.ProductosId, "", new { @class = "text-danger" })
            </div>
        </div>

        <div class="form-group">
            @Html.LabelFor(model => model.Cantidad, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.Cantidad, new { htmlAttributes = new { @class = "form-control" } })
                @Html.ValidationMessageFor(model => model.Cantidad, "", new { @class = "text-danger" })
                @Html.
            </div>
        </div>


        <div class="form-group">
            <div class="col-md-offset-2 col-md-10">
                <input type="submit" value="Create" class="btn btn-default" />
            </div>
        </div>
    </div>
}

<div>
    @Html.ActionLink("Back to List", "Index")
</div>

@section Scripts {
    @Scripts.Render("~/bundles/jqueryval")
}