Hints

from django.contrib.auth import get_user_model
    User = get_user_model()
for u in User.objects.all():
    print(u)
u = User.objects.get(pk=80)
print(u.wagtail_userprofile.submitted_notifications)
u.wagtail_userprofile.submitted_notifications = False
u.wagtail_userprofile.save()