Comment réparer Field définit une relation avec le modèle 'auth.User', qui a été remplacé

J'essaie de changer mon modèle d'utilisateur en un modèle personnalisé. Cela ne me dérange pas de laisser tomber ma base de données et d'en utiliser une nouvelle, mais lorsque j'essaye d'exécuter makemigrations, j'obtiens cette erreur

from django.db import models
from django.contrib.auth.models import User

# Create your models here.
class Session(models.Model):
    session_title = models.CharField(max_length=300)
    session_time = models.DateTimeField("Time of session")
    session_difficulty = models.CharField(max_length=200)
    session_duration = models.IntegerField() 
    session_description = models.TextField()
    session_client = models.ManyToManyField(User, blank=True) 

    def __str__(self):
        return self.session_title   

booking / views.py

INSTALLED_APPS = [
    #Custom apps
    'mainapp.apps.MainappConfig',
    'bookings.apps.BookingsConfig',

    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
]

AUTH_USER_MODEL = 'mainapp.CustomUser'

settings.py

from django.shortcuts import render, get_object_or_404
from django.http import HttpResponse, HttpResponseRedirect
from bookings.models import Session
from django.contrib.auth.decorators import login_required
from django.contrib.auth.models import User

# Create your views here.

def book(request, Session_id):
    lesson = get_object_or_404(Session, pk=Session_id)
    try:
        client = request.user.id
    except (KeyError, Choice.DoesNotExist):
        return render(request, 'booking/details.html', {
            'lesson': lesson,
            'error_message': "You need to login first",
        })
    else:
        lesson.session_client.add(client)
         lesson.save()
     return HttpResponseRedirect("")

réservations / modèles.py

bookings.Session.session_client: (fields.E301) Field defines a relation with the model 'auth.User', which has been swapped out.
        HINT: Update the relation to point at 'settings.AUTH_USER_MODEL'.

J'essaye de changer le modèle d'utilisateur en abstractuser.