Hi,
Have a look at the "migrate.py inspectdb" command documentation (https://docs.djangoproject.com/fr/2.1/ref/django-admin/#inspectdb).
This command generates the models for tables in an existing DB. To avoid messing with the existing data, these models are declared as non managed, which means that the tables are not created nor modified by the migration process.
It should give you a good starting point.
Regards
Eric