Ok, you solved problem, but let's make the post worth while by passing on the usual round of "wisdom". Consider:

#!/usr/bin/perl
# chess.plx
use warnings;
use strict;

use utf8;

my $filename = "thaikjv-fixed.txt";

open my $fIn, '<', $filename or die "Can't open $filename: $!\n";
binmode ($fIn, ":utf8");

while (defined (my $line = <$fIn>)) {
    next if $line !~ /^@(...\d\d\d)/;
    
    my $outname = "$1.html";
    
    open my $fOut, '>', $outname or die "Can't create $outname: $!\n";
    binmode ($fOut, ":utf8");
    print $fOut $line;
    print "hi";
    close $fOut;
}
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Note:

• use three parameter version of open and lexical file handles
• show the file name in errors
• use a while loop instead of a for loop when reading files
• use early exit to avoid extra levels of indentation
• avoid using the default variable across multiple lines