Delete button code using checkbox

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C#

ASP.NET

Visual-Studio

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;

namespace Iselibrary
{
public partial class Delete : Form
{
SqlConnection vid = new SqlConnection("Data Source=.;Initial Catalog=iselibrary;Integrated Security=True");
//private object item;

public Delete()
{
InitializeComponent();
}
private void bindingNavigatorDeleteItem_Click(object sender, EventArgs e)
{

}

private void button1_Click_1(object sender, EventArgs e)
{
this.Close();
Home home = new Home();
home.Show();
}

private void Update_Load(object sender, EventArgs e)
{
// TODO: This line of code loads data into the 'iselibraryDataSet1.T_BOOK_ISSUE_TABLE' table. You can move, or remove it, as needed.
this.t_BOOK_ISSUE_TABLETableAdapter.Fill(this.iselibraryDataSet1.T_BOOK_ISSUE_TABLE);

}

private void button2_Click(object sender, EventArgs e)
{
String str = "Select * from T_BOOK_ISSUE_TABLE where (USN like '%' + @search + '%')";
SqlCommand xp = new SqlCommand(str, vid);
xp.Parameters.Add("@search", SqlDbType.NVarChar).Value = textBox1.Text;


vid.Open();
xp.ExecuteNonQuery();
SqlDataAdapter da = new SqlDataAdapter();
da.SelectCommand = xp;
DataSet dat = new DataSet();
da.Fill(dat, "USN");
dataGridView1.DataSource = dat;
dataGridView1.DataSource = dat.Tables[0];
vid.Close();
}

private void textBox1_TextChanged(object sender, EventArgs e)
{

}
// Delete Button Details//
private void button3_Click(object sender, EventArgs e)
{
iselibraryEntities ise = new iselibraryEntities();
foreach (var item in dataGridView1.Rows)
{
DataGridViewRow row = item as DataGridViewRow;
if (row.Selected)
{
string usn = row.Cells["USN"].Value.ToString();
var issu = ise.T_BOOK_ISSUE_TABLE.FirstOrDefault(a => a.USN.Equals(usn));
if (issu != null)
{
ise.T_BOOK_ISSUE_TABLE.Remove  /* as error occurs here I have not completed the code*/
}
}
}
}

private void dataGridView1_CellContentClick(object sender, DataGridViewCellEventArgs e)
{

}
}
}

THANK YOU

As soon as i complete ise.T_BOOK_ISSUE_TABLE. in If loop, I dont get a dropdown for Remove. Why so? and error says as:'Object Query<T_BOOK_ISSUE_TABLE>' does not contain a definition for 'remove' and no extension method 'remove' accepting a first argument of type'Object Query<T_BOOK_ISSUE_TABLE>'could be found(are you missing a directive or an assembly reference?)
Please let me know where im going wrong or anyone out there please help me to write delete button code using checkbox checked.(#windows form app) Hope anyone in forum helps....
Thank you