Django course code error

hello, today i got to the orm part of the course. i needed to delete my code and install it from the resources to make sure I have the same code. after I installed it and reseted the database when Iran the server I got this error when I tried to open localhost:8000/playground/hello :
RuntimeError at /playground/hello/
Model class django.contrib.sessions.models.Session doesn’t declare an explicit app_label and isn’t in an application in INSTALLED_APPS.

how can I fix it?

might be you forgot to add session in installed_apps which mosh let us deleted in first chapter