test.dat:

1START   ACCOUNTA     XXXXXMA      12345     XYZ111          1START   
+ACCOUNTB     XXXXXBR      12345     XYZ191          1START   ACCOUNTA
+     XXXXXNY      54321     XYZ131
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code:

#!/usr/bin/perl

use strict;
use warnings;

use Data::Dumper;

$| = 1;
srand();
$Data::Dumper::Sortkeys = 1;

my $fn = q{test.dat};
open my $df, $fn or die $!;
$/ = q{1START};
while ( my $line = <$df> ) {
    chomp $line;
    next if ( $line =~ m/^\s*$/ );

    if ( substr( $line, 3, 8 ) eq q{ACCOUNTA} ) {
        print $/, $line, qq{\n};
    }
}
close $df;
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output:

1START   ACCOUNTA     XXXXXMA      12345     XYZ111
1START   ACCOUNTA     XXXXXNY      54321     XYZ131
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