This is slightly more complicated than your average hash walker, since we need to know how to modify the parent. This solution passes around an $extra hash with information on how to update the parent. $extra is expected to have keys parent and key. Based on the ref of parent, we update it as a hash or an array. We could make this a bit cleaner by a closure as the extra argument, and we call the closure when we find a match.

#!/usr/bin/perl -w

use strict;
use Data::Dumper;
use Test::More tests => 1;

my $element = {
          'check' => {
                     'field' => 'OLK_BO_BK_TYPE'
                   },
          'type' => 'case',
          'case' => [
                    {
                      'value' => '1',
                      'resultset' => 'BROKER'
                    },
                    {
                      'value' => '3',
                      'resultset' => {
                                      'field' => 'OLK_BO_BK_DESC'
                                     },
                    },
                  ]
        };

my $expected = {
          'check' => 'OLK_BO_BK_TYPE',
          'type' => 'case',
          'case' => [
                    {
                      'value' => '1',
                      'resultset' => 'BROKER'
                    },
                    {
                      'value' => '3',
                      'resultset' => 'OLK_BO_BK_DESC',
                    },
                  ]
        };

hash_walk($element);
is_deeply( $element, $expected, "hash_walk worked as expected");

sub hash_walk {
    my ( $element, $extra ) = @_;
    my ( $parent, $pkey );
    if ($extra) {
        $parent = $extra->{parent};
        $pkey   = $extra->{key};
    }

    if ( ref($element) =~ /HASH/ ) {
        foreach my $key ( keys %$element ) {
            if ( $key =~ /field/ ) {
                if ( ref($parent) eq 'HASH' ) {
                    $parent->{$pkey} = $element->{$key};
                }
                elsif ( ref( $parent eq 'ARRAY' ) ) {
                    $parent->[$pkey] = $element->{$key};
                }
                else {
                    warn("I don't know what to do with field in parent
+[$parent]"
                    );
                }
            }
            else {
                hash_walk( $element->{$key},
                    { parent => $element, key => $key } );
            }
        }
    }
    elsif ( ref($element) =~ /ARRAY/ ) {
        my $upper = @$element - 1;
        foreach my $i ( 0 .. $upper ) {
            my $index = $element->[$i];
            hash_walk( $index, { parent => $element, key => $i } );
        }
    }
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