namespace Customize\Entity;
use Doctrine\ORM\Mapping as ORM;
use Eccube\Annotation\EntityExtension;
use Symfony\Component\Validator\Constraints as Assert;
trait CustomerTrait
{
    /**
     * @var string|null
     * @ORM\Column(name="batting_style", type="string", length=255, nullable=true)
     * @EntityExtension\FormAppend(
     *     auto_render=false,
     *     type="\Symfony\Component\Form\Extension\Core\Type\ChoiceType",
     *     options={
     *          "label": "右／左",
     *          "choices": {
     *              "右": "right",
     *              "左": "left"
     *          },
     *          "required": false,
     *          "expanded": true,
     *          "multiple": false,
     *          "mapped": true
     *     }
     * )
     */
    private $battingStyle;

    /**
     * @var string|null
     * @ORM\Column(name="average_score", type="string", length=255, nullable=true)
     * @EntityExtension\FormAppend(
     *     auto_render=false,
     *     type="\Symfony\Component\Form\Extension\Core\Type\ChoiceType",
     *     options={
     *          "label": "平均スコア",
     *          "choices": {
     *              "A": "A",
     *              "B": "B",
     *              "C": "C",
     *              "D": "D",
     *              "E": "E"
     *          },
     *          "required": false,
     *          "expanded": true,
     *          "multiple": false,
     *          "mapped": true
     *     }
     * )
     */
    private $averageScore;

    public function getBattingStyle()
    {
        return $this->battingStyle;
    }

    public function setBattingStyle($battingStyle)
    {
        $this->battingStyle = $battingStyle;
        return $this;
    }

    public function getAverageScore()
    {
        return $this->averageScore;
    }

    public function setAverageScore($averageScore)
    {
        $this->averageScore = $averageScore;
        return $this;
    }
}

namespace Customize\Form\Extension;

use Symfony\Component\Form\AbstractTypeExtension;
use Symfony\Component\Form\Extension\Core\Type\ChoiceType;
use Symfony\Component\Form\FormBuilderInterface;
use Eccube\Form\Type\Front\MypageChangeType;

class MypageChangeTypeExtension extends AbstractTypeExtension
{
    public static function getExtendedTypes(): iterable
    {
        return [MypageChangeType::class];
    }

    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('battingStyle', ChoiceType::class, [
                'label' => '右／左',
                'choices' => [
                    '右' => 'right',
                    '左' => 'left',
                ],
                'expanded' => true,
                'multiple' => false,
                'required' => false,
            ])
            ->add('averageScore', ChoiceType::class, [
                'label' => '平均スコア',
                'choices' => [
                    'A' => 'A',
                    'B' => 'B',
                    'C' => 'C',
                    'D' => 'D',
                    'E' => 'E',
                ],
                'required' => false,
            ]);
    }
}

namespace Eccube\Entity;
// 既存のコード...
use Customize\Entity\CustomerTrait; //  追加
/**
// 既存のコード...
 */
class Customer extends \Eccube\Entity\AbstractEntity implements UserInterface, \Serializable
{
    use CustomerTrait; // 追加
    // 既存のコード...
}

◯src/Eccube/Entity/Customer.php　修正

◯app/config/eccube/services.yaml