Hi Jeonghan,
Try leaving the organization:
Leave an organization as an external user
https://learn.microsoft.com/en-us/entra/external-id/leave-the-organization
You can usually leave an organization on your own without having to contact an administrator. However, in some cases this option won't be available and you'll need to contact your tenant admin, who can delete your account in the external organization. This article is intended for administrators. If you're a user looking for information about how to manage and leave an organization, see the Manage organizations article.
If this is helpful please accept answer.