Thank you for posting this in Microsoft Q&A.
As I understand you want to delete remove the tenant in your Entra ID free version environment.
Admin password has been changed accidently and currently you do not remember the password.
Currently you do not have access to the tenant to remove the environment.
In this situation first you will have to gain access to your tenant by getting the global admin password reset.
If there is only one global admin account in your tenant and it is blocked entirely, you can reach out to our support team. You can look into below article to get support numbers depending on your country.
or creating a ticket through a different account: https://learn.microsoft.com/en-us/microsoft-365/admin/get-help-support?view=o365-worldwide#phone-support
Create a ticket with Microsoft support team. Give them the tenant ID which is locked out in your description. Tell them that no admin account has access anymore and your partners also have no access anymore.
Once you create a ticket with support team you will have to work with our data protection team. You will have to first prove your identity against your tenant for security purpose. Post that this team will help you with help you in getting access to your tenant or unlock your account depending on your scenario.
Also, for the future, you can create an emergency access account (break glass) in Azure AD. This account will help prevent being accidentally locked out of your Azure Active Directory (Azure AD) organization because you can't sign in for any reason.
https://docs.microsoft.com/en-us/azure/active-directory/roles/security-emergency-access
Problems with two-step verification for Azure B2C accounts - Microsoft Q&A
Once you have the Global Admin password reset or once you have access to the tenant you can follow below article to remove the directory.
https://learn.microsoft.com/en-us/entra/identity/users/directory-delete-howto
Let me know if you have any further questions.
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