my $oldworkbook;
if(-e $filename) {
    $oldworkbook = Spreadsheet::ParseExcel::Workbook->Parse($filename);        
}

my $workbook = Spreadsheet::WriteExcel->new($filename);
if(defined $oldworkbook) {
    for(my $i = 0; $i < $oldworkbook->{SheetCount}; $i++) {
        
        my $ws = $oldworkbook->{Worksheet}[$i];
        
        my $worksheet = $workbook->add_worksheet($ws->{Name});
        for(my $row = $ws->{MinRow}; defined $ws->{MaxRow} && $row <= $ws->{MaxRow}; $row++) {
            for(my $col = $ws->{MinCol}; defined $ws->{MaxCol} && $col <= $ws->{MaxCol}; $col++) {
                my $cell = $ws->{Cells}[$row][$col];
                $worksheet->write($row, $col, $cell->Value);
            }
        }
    }
}

$worksheet->write($row, $col, $cell->Value) 
  if defined $cell;