Deleting data from database using gridview checkbox and button

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ASP.NET

SQL

Gridview

database

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Hello everybody I have a question this is my populating data codes

public void Populateicerik()
        {
            string bag = WebConfigurationManager.ConnectionStrings["AdminPanel.Properties.Settings.ConnStr"].ConnectionString;
            SqlConnection con = new SqlConnection(bag);

            string komut = "select icerikID,KBaslik,icerikDurum,icerikErisim,icerikMetin from icerik inner join kategoriler on KID = KategoriID";
            SqlCommand cmd = new SqlCommand(komut, con);

            SqlDataAdapter adp = new SqlDataAdapter(cmd);
            DataTable dt = new DataTable();
            adp.Fill(dt);
            GridView3.DataSource = dt;
            GridView3.DataBind();
            con.Open();
            con.Close();

            GridView3.HeaderRow.Cells[1].Text = "iID";
            GridView3.HeaderRow.Cells[2].Text = "Kategori";
            GridView3.HeaderRow.Cells[3].Text = "Durum";
            GridView3.HeaderRow.Cells[4].Text = "Erişim";
            GridView3.HeaderRow.Cells[5].Text = "İçerik";
        }

and this delete codes
protected void LinkButton2_Click(object sender, EventArgs e)
        {
            foreach (GridViewRow row in GridView3.Rows)
            {
                var chk = row.FindControl("Chk") as CheckBox;

                if (chk.Checked)
                {
                    string bag = WebConfigurationManager.ConnectionStrings["AdminPanel.Properties.Settings.ConnStr"].ConnectionString;
                    SqlConnection con = new SqlConnection(bag);

                    SqlCommand cmd = new SqlCommand("icerik_Delete", con);
                    cmd.CommandType = CommandType.StoredProcedure;
                    
                    cmd.Parameters.AddWithValue("icerikID", GridView3.SelectedRow.Cells[1].Text);
                    con.Open();
                    cmd.ExecuteNonQuery();
                    con.Close();
                }
            }
        }

this is not working gridview3.selectedrow turns as null what shoul I do to make it correct please help thank you .