Errors after django 1.7 migration and reset

Question

*This is my first time learning back-end development, so please bear with me.

I am working on an app named "Taskmanger" with Django 1.7. After performing inital migration with following commands.

python manage.py makemigrations Taskmanager
python manage.py migrate

I got the following error when I tried to run runserver command.

   File"/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/importlib/__init__.py", line 37, in import_module
    __import__(name)
    ImportError: No module named adminTaskmanager

and deleting migration files

Then, I deleted the migration folder and files inside the app folder, and now I am getting duplicate error:

django.core.exceptions.ImproperlyConfigured: Application labels aren't unique, duplicates: admin

Could anyone tell me how I can go back to the time point before I ran migrate commands? (I am not looking for answers on how to override the duplicate error.)