You're almost there.
bvnFeilds (bvnFields?) is not re-instantiated within the loop. You have one single instance that gets rewritten every loop. I have corrected below
using (OracleConnection connection = new OracleConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString))
{
DataTable dt = new DataTable();
OracleCommand command = new OracleCommand(select, connection);
command.CommandTimeout = 900000000;
DataSet dataset = new DataSet();
OracleDataAdapter adapter = new OracleDataAdapter(command);
adapter.Fill(dataset);
dt = dataset.Tables[0];
List<bvnnotenrolledallbranches> gridRecords = new List<bvnnotenrolledallbranches>();
lblNoRecord.Text = "Total record(s): " + dt.Rows.Count.ToString();
lblNoRecord.ForeColor = System.Drawing.Color.Green;
foreach (System.Data.DataRow dr in dt.Rows)
{
BVNNotEnrolledAllBranches bvnFeilds = new BVNNotEnrolledAllBranches();
bvnFeilds.CustomerName = (dr["Customer_name"].ToString());
bvnFeilds.AccountNumber = (dr["Account_number"].ToString());
bvnFeilds.CIF = (dr["CIF_ID"].ToString());
bvnFeilds.PhoneNumber = (dr["Phone_Number"].ToString());
bvnFeilds.BranchName = (dr["BRANCH_NAME"].ToString());
bvnFeilds.BVN = (dr["BVN"].ToString());
bvnFeilds.Email = (dr["Email"].ToString());
gridRecords.Add(bvnFeilds);
}
GridView1.DataSource = gridRecords;
GridView1.DataBind();
}
</bvnnotenrolledallbranches></bvnnotenrolledallbranches>