Try this, it should list the SERIES data for all the charts in the workbook.
If it does then the code I have commented out may be all you need to make the changes.

#!perl
use strict;
use Win32::OLE::Const 'Microsoft Excel';
Win32::OLE->Option(Warn => 3);

my $ex = Win32::OLE->GetActiveObject('Excel.Application')
        || Win32::OLE->new('Excel.Application', 'Quit');
        
# change filename to suit
my $wb = $ex->Workbooks->Open('c:/temp/testchart.xls') ; 

for my $ws ( $wb->Sheets->in){
  print "\nSheet = ".$ws->Name."\n";
  for my $obj ( $ws->ChartObjects->in ){
    my $cht = $obj->Chart;
    print "Name  = ".$cht->Name."\n";
    print "Title = ".$cht->ChartTitle->text."\n" if $cht->hasTitle;
    for my $ser ($cht->SeriesCollection->in){
      my $SERIES = $ser->{'FormulaR1C1'};
      print $ser->Name.' ['.$SERIES."]\n";   
       # make changes as appropriate
       #my $NEWSERIES = $SERIES;
       #if ($NEWSERIES =~ s/Sheet1/Sheet2/g){;
       #  $ser->{'FormulaR1C1'} = $NEWSERIES;
       #  print "--> Changed to [$NEWSERIES]\n";
       #};
    }
  }
}
# save and exit
$wb->SaveAs( 'c:\\temp\\changed.xls' );
undef $wb;
undef $ex;
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poj