Massively complex but working never the less.

app/Helpers/Csv/Converter/OpposingAccountIban.php

@@ -0,0 +1,39 @@
+<?php
+
+namespace FireflyIII\Helpers\Csv\Converter;
+
+use Auth;
+use FireflyIII\Models\Account;
+
+/**
+ * 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()
+    {
+        if (isset($this->mapped[$this->index][$this->value])) {
+            $account = Auth::user()->accounts()->find($this->mapped[$this->index][$this->value]);
+
+            return $account;
+        } else {
+            $set = Auth::user()->accounts()->get();
+            /** @var Account $account */
+            foreach ($set as $account) {
+                if ($account->iban == $this->value) {
+                    return $account;
+                }
+            }
+
+            return $this->value;
+        }
+    }
+}