firefly-iii/app/Helpers/Csv/Converter/OpposingAccountIban.php

<?php
declare(strict_types = 1);
namespace FireflyIII\Helpers\Csv\Converter;

use FireflyIII\Models\Account;
use FireflyIII\Repositories\Account\AccountRepositoryInterface;

/**
 * Class OpposingAccountIban
 *
 * @package FireflyIII\Helpers\Csv\Converter
 */
class OpposingAccountIban extends BasicConverter implements ConverterInterface
{

    /**
     * If mapped, return account. Otherwise, only return the name itself.
     *
     * @return Account|string
     */
    public function convert()
    {
        /** @var AccountRepositoryInterface $repository */
        $repository = app('FireflyIII\Repositories\Account\AccountRepositoryInterface');

        if (isset($this->mapped[$this->index][$this->value])) {
            $account = $repository->find($this->mapped[$this->index][$this->value]);

            return $account;
        } else {
            if (strlen($this->value) > 0) {

                $set = $repository->getAccounts([]);
                /** @var Account $account */
                foreach ($set as $account) {
                    if ($account->iban == $this->value) {

                        return $account;
                    }
                }
            }

            return $this->value;
        }
    }

}