This is not the most efficient way, but it seems to work.

gistfile1.pl

#!/usr/bin/env perl

use Koha;
use C4::Context;
use C4::Reserves;
use C4::Circulation;
use C4::Items;

my $dbh = C4::Context->dbh;
my $itemnumbers = $dbh->selectcol_arrayref(
    q{SELECT itemnumber FROM items
      WHERE biblionumber IN (
        SELECT DISTINCT biblionumber FROM reserves
      )
      ORDER BY itemnumber}
    );

for (@$itemnumbers) {
    my $item = C4::Items::GetItem($_);
    my ($status, $reserve) = C4::Reserves::CheckReserves($_);
    next unless $status ~~ 'Reserved';

    my (undef, $message, undef, undef)
        = C4::Circulation::AddReturn($item->{barcode}, $item->{homebranch});
    next if not $message->{ResFound};

    my $borrower = C4::Members::GetMember($reserve->{borrowernumber});
    my $biblio = C4::Biblio::GetBiblioData($reserve->{biblionumber});
    my $queue_entry = {
        reservenumber => $reserve->{reservenumber},
        biblionumber => $reserve->{biblionumber},
        itemnumber => $item->{itemnumber},
        barcode => $item->{barcode},
        surname => $borrower->{surname},
        borrowernumber => $borrower->{borrowernumber},
        reservedate => $reserve->{reservedate},
        title => $biblio->{title},
        itemcallnumber => $biblio->{cn_class},
        holdingbranch => $item->{homebranch},
        pickbranch => $borrower->{branchcode},
    };
    C4::Reserves::SaveHoldInQueue(%$queue_entry);
}