open my $infh, "<", "old.txt" or die $!;
open my $outfh, ">", "new.txt" or die $!;
<$infh>; # Discard the first line
while (<$infh>) {
   chomp;
   s/\t/\n/;
   print {$outfh} "$_\n";
}
close $infh;
close $outfh;