Delete button code using checkbox

// 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
} 
}
}
Thing is I don't get a dropdown for remove in if loop after ise.T_BOOK_ISSUE_TABLE.

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?)
How to get rid of this error?