If you really wanted to change split, you could use an array slice like ar0n demonstrated, but applying it directly to split instead of @Fld ...

my @Fld = ( split /\t/ )[0,4];
my $col = 0;
foreach my $token (@Fld) {
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Another way, is to loop over the indicies you want...

my @fld_no = qw( 0 4 );
my $row    = 0;
 # ...
  foreach my $idx (@fld_no) {
    $worksheet->write($row, $col, $fld[$idx]);
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    --k.