ServiceForm.php

<?php
namespace App\Forms\Entities;

use App\Forms\YamlConfigForm as Form;
use App\Models\Agency;
use App\Models\Service;

class ServiceForm extends Form
{
    public function getModelClass()
    {
        return Service::class;
    }

    public function buildForm()
    {
        $data = $this->getRequest();

        parent::buildForm();
        $this->addBefore('Type', 'AgencyId', 'static', [
                'value' => function ($value) use ($data) {
                    return $value ? Agency::find($value)->Name : null;
                }
            ])
        ;
    }
}