Before enabling this you must:
You can input relative path here
Feel free to adjust the priv_dir and port number. Then you will have to create the key for the keys (in the example priv/ssh_keys) and create the host keys with ssh-keygen -m PEM -N "" -b 2048 -t rsa -f ssh_host_rsa_key. After restarting, you should be able to connect to your Pleroma instance with ssh username@server -p $PORT