Hi Ruben12345,

Check this example. Now please take its reference and implemented in your code.

SQL

CREATE PROCEDURE [dbo].[Customers_InsertUpdate]
      @CustomerId INT = NULL
      ,@Name VARCHAR(100) = NULL
      ,@Country VARCHAR(100) = NULL
AS
BEGIN
      SET NOCOUNT ON;

	IF EXISTS(SELECT CustomerId FROM Customers WHERE CustomerId = @CustomerId)
	BEGIN
		UPDATE Customers
		SET Name = @Name, Country = @Country
		WHERE CustomerId = @CustomerId
	END
	ELSE
	BEGIN
		INSERT INTO Customers(Name, Country) VALUES (@Name, @Country)		
	END   
END

Namespaces

using System.Data;
using System.Data.OleDb;
using System.Data.SqlClient;
using System.Configuration;

Controller

public class HomeController : Controller
{
    // GET: /Home/
    public ActionResult Index()
    {
        return View();
    }

    [HttpPost]
    public ActionResult Import()
    {
        string filePath = Server.MapPath("~/Files/Customers.xlsx");
        string conString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source={0};Extended Properties='Excel 8.0;HDR=YES'";

        DataTable dt = new DataTable();
        conString = string.Format(conString, filePath);
        using (OleDbConnection connExcel = new OleDbConnection(conString))
        {
            using (OleDbCommand cmdExcel = new OleDbCommand())
            {
                using (OleDbDataAdapter odaExcel = new OleDbDataAdapter())
                {
                    cmdExcel.Connection = connExcel;
                    //Get the name of First Sheet.
                    connExcel.Open();
                    DataTable dtExcelSchema;
                    dtExcelSchema = connExcel.GetOleDbSchemaTable(OleDbSchemaGuid.Tables, null);
                    string sheetName = dtExcelSchema.Rows[0]["TABLE_NAME"].ToString();
                    connExcel.Close();
                    //Read Data from First Sheet.
                    connExcel.Open();
                    cmdExcel.CommandText = "SELECT * From [" + sheetName + "]";
                    odaExcel.SelectCommand = cmdExcel;
                    odaExcel.Fill(dt);
                    connExcel.Close();
                }
            }
        }
        foreach (DataRow row in dt.Rows)
        {
            int id = Convert.ToInt32(row["CustomerId"]);
            string name = Convert.ToString(row["Name"]);
            string country = Convert.ToString(row["Country"]);
            using (SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["constr"].ConnectionString))
            {
                using (SqlCommand cmd = new SqlCommand("Customers_InsertUpdate"))
                {
                    cmd.CommandType = CommandType.StoredProcedure;
                    cmd.Parameters.AddWithValue("@CustomerId", id);
                    cmd.Parameters.AddWithValue("@Name", name);
                    cmd.Parameters.AddWithValue("@Country", country);
                    cmd.Connection = con;
                    con.Open();
                    cmd.ExecuteNonQuery();
                    con.Close();
                }
            }
        }

        return View("index");
    }
}

View

<div>
    <% using (Html.BeginForm("Import", "Home", FormMethod.Post))
        { %>
    <input type="submit" value="Save" id="btnSave" />
    <% } %>
</div>

If you don't want to use loop the you can use SqlBulkCopy class to do so.

For this refer below article.

SqlBulkCopy- Bulk Insert records and Update existing rows if record exists using C# and VB.Net