Aside from what moritz said, do you really need to have $part1 and $part2? Since you are parsing an array you'll have to go through the process of running all its values. There are quite a few ways to do that. You can

use the for loop to build the final string to be printed, and print it outside the block

@l=<F3>;
my $text = '';
for my $line (@l){
    chomp $line;
    my ($part1, $part2) = split /\*/,$line;
    $text .= "$part1 $part2\n";
}

print $text;
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create the single string right from the array values by joining them

@l=<F3>;
my $text = join '', @l;
$text =~ s/\*/ /g;
print $text;
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use a different kind of block

@l=<F3>;
print map {s/\*/ /;$_;} @l;
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