Something similar to this would work.

use Text::CSV;

use warnings;
use strict;

# Reading the first file and extracting IVAL...S

my $csv = Text::CSV->new;
my @header = $csv->getline(\*DATA);
$csv->column_names(@header);

my $frst = $csv->getline_hr(\*DATA);
my ($ivaldate, $ivalstart, $ivalend) = map { $frst->{$_} } qw( IVALDAT
+E IVALSTART IVALEND );

# Reading all the rest
my $line = <DATA>;
$line =~ s/,/\t/g;
print join "\t", qw( Date StartTime EndTime), $line;
while ($line = <DATA>) {
    $line =~ s/,/\t/g;
    print join "\t", $ivaldate, $ivalstart, $ivalend, $line;
}

__DATA__
"CLLI","SWREL","RPTDATE","RPTIME","TZ","RPTTYPE","RPTPD","IVALDATE","I
+VALSTART","IVALEND","NUMENTIDS"
"toroonxn0dw","EAGLE5 40.1.0-62.13.19","2009-11-13","19:00:23","EST ",
+"STP SYSTEM TOTAL MEASUREMENTS ON TT","LAST","2009-11-13","18:45:00",
+"19:00:00",256
"STATUS","TT","GTTPERFD","GTTUN0NS","GTTUN1NT","AGTTPERFD"
"K","0",0,0,0,0
"K","1",0,0,0,0
"K","2",0,0,0,0
"K","3",0,0,0,0
"K","4",0,0,0,0
"K","5",0,0,0,0
"K","6",0,0,0,0
"K","7",0,0,0,0
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