Generally the convention is to copy a custom config into sites-available and then link to it from sites-enabled.
What I think you should do here is

* rm the symlink /etc/nginx/sites-enabled/default to remove the default config (assuming you don't want it)
* create `/etc/nginx/sites-available/machine-learning` or a config with a similar name that has what you want in it
* link `/etc/nginx/sites-enabled/machine-learning` to `/etc/nginx/sites-available/machine-learning` to activate it