how to run execute reader

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C#

i have following code

 OdbcCommand Command = MainClass.Conn.CreateCommand();
  Command.Connection = MainClass.Conn;
  
  using (OdbcTransaction transaction = MainClass.Conn.BeginTransaction())
            {
                Command.Transaction = transaction;
                try
                {
                    string saveStOpen = "Insert Statement.. "; \\ This This Is SQL Statement
                    Command.CommandText = saveStOpen;
                    Command.ExecuteNonQuery();

                    string saveGRNSub = "Insert Statement.."; \\ This This Is SQL 
                    Command.CommandText = saveGRNSub;
                    Command.ExecuteNonQuery();

                    OdbcCommand OpenTemp = new  OdbcCommand("SELECT * FROM GRN_TEMP WHERE (UserName = '" + MainClass.GetComputerName() + "')", MainClass.Conn);
                    OdbcDataAdapter da = new OdbcDataAdapter(OpenTemp);
                    DataTable dt = new DataTable();
                    da.Fill(dt); \\ This Point Genarate An Error 

                    if (dt.Rows.Count >0)
                    {
                        MessageBox.Show(dt.Rows.Count.ToString());
                    }
                    
                    
                    //}
                    //readTemp.Dispose();
                    
                    transaction.Commit();

at da.Fill(dt);

Generate Error (executereader requires the command to have a transaction )

how to avoid this error

I highly appreciate in advance