the code you gave me throws this error :System.ArgumentException: 'Column named Appliance cannot be found.
line where error occurs :string applianceInGrid = dataGridView1.Rows[i].Cells["Appliance"].Value.ToString();

rest of my code:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Runtime.Remoting.Lifetime;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
using System.Windows.Forms;
using static System.Net.Mime.MediaTypeNames;
using static System.Windows.Forms.VisualStyles.VisualStyleElement;
using System.Text.RegularExpressions;
using static System.Windows.Forms.VisualStyles.VisualStyleElement.TextBox;

namespace ApplianceRental
{
    public partial class CustomerDashboardForm : Form
    {
        private DataTable cartItems = new DataTable();
        public CustomerDashboardForm()
        {
            InitializeComponent();
            cartItems.Columns.Add("Appliance");
            cartItems.Columns.Add("PowerUsage");
            cartItems.Columns.Add("TypicalUsage");
            cartItems.Columns.Add("AnnualCost");
            // Set dataGridViewCart DataSource
            dataGridViewCart.DataSource = cartItems;
        }

        private void CustomerDashboardForm_Load(object sender, EventArgs e)
        {
            // TODO: This line of code loads data into the 'db_usersDataSet.ApplianceDBLIST' table. You can move, or remove it, as needed.
            this.applianceDBLISTTableAdapter.Fill(this.db_usersDataSet.ApplianceDBLIST);
            BindingSource bindingSource = new BindingSource();
            bindingSource.DataSource = this.db_usersDataSet.ApplianceDBLIST;
            comboBox1.DataSource = bindingSource;
            comboBox1.DisplayMember = "Appliance";  // replace “Appliance” with your actual appliance column name
        }

        private void dataGridView1_CellContentClick(object sender, DataGridViewCellEventArgs e)
        {

        }

        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            for (int i = 0; i < dataGridView1.Rows.Count; i++)
            {
                string applianceInGrid = dataGridView1.Rows[i].Cells["Appliance"].Value.ToString();
                string applianceInComboBox = comboBox1.SelectedItem.ToString();

                if (applianceInGrid == applianceInComboBox)
                {
                    dataGridView1.ClearSelection();
                    dataGridView1.Rows[i].Selected = true;
                    dataGridView1.CurrentCell = dataGridView1.Rows[i].Cells[0];
                    break;
                }
            }
            }
        private void CalculateTotal()
        {
            decimal totalAmount = 0;

            foreach (DataRow row in cartItems.Rows)
            {
                totalAmount += Convert.ToDecimal(row["AnnualCost"]);
            }

            labelTotalAmount.Text = "Total Amount: " + totalAmount.ToString("C");
        }
        private void button1_Click(object sender, EventArgs e)
        {
            if (dataGridView1.SelectedRows.Count < 1)
            {
                MessageBox.Show("Please select an appliance to add to the cart.");
                
            }
            // Get the selected row in dataGridView1
            DataGridViewRow selectedRow = dataGridView1.SelectedRows[0];

            // Create a new row for cartItems
            DataRow newRow = cartItems.NewRow();

            newRow["Appliance"] = selectedRow.Cells["Appliance"].Value;
            newRow["Power Usage"] = selectedRow.Cells["Power Usage"].Value;
            newRow["Typical Usage"] = selectedRow.Cells["Typical Usage"].Value;
            newRow["Estimated Annual Costs"] = selectedRow.Cells["Estimated annual running costs"].Value;

            // Add newRow to the cartItems
            cartItems.Rows.Add(newRow);

            // Calculate and display the total amount
            CalculateTotal();
        }
       
        private void searchBox_TextChanged(object sender, EventArgs e)
        {
        }

        private void button2_Click(object sender, EventArgs e)
        {
            if (string.IsNullOrEmpty(searchBox.Text))
            {
                MessageBox.Show("Please enter something to search");
            }
            else
            {
                DataView dataView = db_usersDataSet.ApplianceDBLIST.DefaultView;
                string searchExpression = Regex.Escape(searchBox.Text.Trim()).Replace("'", "''");
                dataView.RowFilter = string.Format("Appliance LIKE '%{0}%'", searchExpression);
                dataGridView1.DataSource = dataView;
            }
        }
    }
}