To delete an application, be listed as an owner of the application or have admin privileges.
Sign in to the Azure portal.
If you have access to multiple tenants, use the Directory + subscription filter in the top menu to select the tenant in which the app is registered.
Search and select the Azure Active Directory.
Under Manage, select App registrations and select the application that you want to configure.
Once you've selected the app, you'll see the application's Overview page.
From the Overview page, select Delete.
Read the deletion details. Check the box if one appears at the bottom of the pane.
Select Delete to confirm that you want to delete the app.
Microsoft KB Article: https://learn.microsoft.com/en-us/azure/active-directory/develop/howto-remove-app