After you delete an app registration, the app remains in a suspended state for 30 days. During that 30-day window, the app registration can be restored, along with all its properties. After that 30-day window passes, app registrations can’t be restored, and the permanent deletion process may be automatically started. This functionality only applies to applications associated to a directory. It isn’t available for applications from a personal Microsoft account, which can’t be restored.
You can view your deleted applications, restore a deleted application, or permanently delete an application using the App registrations experience under Azure Active Directory (Azure AD) in the Azure portal.
Neither you nor Microsoft customer support can restore a permanently deleted application or an application deleted more than 30 days ago.
Required permissions
You must have one of the following roles to permanently delete applications.
- Global administrator
- Application administrator
- Cloud application administrator
- Hybrid identity administrator
- Application owner
You must have one of the following roles to restore applications.
- Global administrator
- Application owner
View your deleted applications
You can see all the applications in a soft deleted state. Only applications deleted less than 30 days ago can be restored.
To view your restorable applications
- Sign in to the Azure portal.
- Search and select Azure Active Directory, select App registrations, and then select the Deleted applications (Preview) tab.
Review the list of applications. Only applications that have been deleted in the past 30 days are available to restore. If using the App registrations search preview, you can filter by the ‘Deleted date’ column to see only these applications.
Restore a recently deleted application
When an app registration is deleted from the organization, the app is in a suspended state, and its configurations are preserved. When you restore an app registration, its configurations are also restored. However, if there were any organization-specific settings in Enterprise applications for the application’s home tenant, those won’t be restored.
This is because organization-specific settings are stored on a separate object, called the service principal. Settings held on the service principal include permission consents and user and group assignments for a certain organization; these configurations won’t be restored when the app is restored. To learn how to restore the service principal with its previous configurations, see Restore a recently deleted enterprise application.
To restore an application
- On the Deleted applications (Preview) tab, search for and select one of the applications deleted less than 30 days ago.
- Select Restore app registration.
Permanently delete an application
You can manually permanently delete an application from your organization. A permanently deleted application can’t be restored by you, another administrator, or by Microsoft customer support.
To permanently delete an application
- On the Deleted applications (Preview) tab, search for and select one of the available applications.
- Select Delete permanently.
- Read the warning text and select Yes.
Ref: https://docs.microsoft.com/en-us/azure/active-directory/develop/howto-restore-app