To reset an app back to the initial “zero” migration:

python manage.py migrate --fake myapp zero

Alternatively, you may want to completely start again.

Delete all migration files:

find . -path "*migrations/*.py" -not -name __init__.py -delete

Now you can recreate the database and migrations:

dropdb mydb; createdb mydb # Recreate postgres
python manage.py makemigrations
python manage.py migrate