Pass data from JTable to Jtable with saved auto

Good friends, I present a problem in my code, the question would be: How do I make it so that when passing data from one table to another, those that were already there are not deleted?

I am passing a selected row from a JTablePendientes to another JTableCompletados in the same Frame through a simple button, these tables are automatically saved in Excel files with the jxl library. In itself I think the problem lies more in that when you restart the application and re-pass data through the button, they are inserted in the first row of the other table, deleting the data that were already.

Here is a bit of code:

This is the Action Listener that passes the row of JTablePendientes to JTable Completed:

menuItemCompletar.addActionListener(new ActionListener() {

        @Override
        public void actionPerformed(ActionEvent e) {
            if(tablaListado.getSelectedRowCount() > 0) {
                 // 1) Obtener los índices de las filas seleccionadas.
                 int[] indices = tablaListado.getSelectedRows();
                 // 2) Para cada fila, crear un Array para guardar los valores. 
                 for(int i : indices) {
                     Object[] fila = new Object[modelo.getColumnCount()];
                     // Guardar los valores de la fila de origen.
                     for(int j = 0; j < fila.length; j++) {
                         fila[j] = modelo.getValueAt(i, j);
                     }
                     // 3) Agregar la fila al TableModel de la tabla de destino
                     modelo2.addRow(fila);
                 }
                 autoGuardado();
             }

This would be the code that saves the tables to an Excel file:

public void autoGuardado() {

        try {
            List<JTable> tb = new ArrayList<JTable>();
            tb.add(JTablePendientes);
            //-------------------
            export_excel excelExporter = new export_excel(tb, new File(EXCEL_FILE_LOCATION));
            excelExporter.export();  // Ejecuta el auto guardado
        } catch (Exception ex) {
            ex.printStackTrace();
        }
        try {
            List<JTable> tb2 = new ArrayList<JTable>();
            tb2.add(JTableCompletos);
            //-------------------
            export_excel excelExporter2 = new export_excel(tb2, new File(EXCEL_FILE_LOCATION2));
            excelExporter2.export();  // Ejecuta el auto guardado
        } catch (Exception ex) {
            ex.printStackTrace();
        }

}

As you can see in the images the rows are passed correctly, but when you restart the application and "Complete" other rows, they are deleted.

Any advice?