Nginx Server Block Always Prefix URL with String

In nginx server block I need to prefix url with country code always.

Example if request comes with example.com, I need it to redirect it to example.com/au Then I have a alias to handle /au location. But if it already comes as example.com/au I don't want this redirection to happen. Any help guys?

server {

    server_name  example.com;

    root   /data/www/public;
    index index.php index.html index.htm;

    error_page 404 /404.html;
    error_page 500 502 503 504 /50x.html;

    location = /50x.html {
        root /usr/share/nginx/html;
    }

    location / {
            try_files $uri $uri/ /index.php?$query_string;
    }



     location /au {
            alias /data/www/public;
            try_files $uri $uri/ @au;
            location ~ \.php$ {
                   include fastcgi_params;
                   fastcgi_param SCRIPT_FILENAME $request_filename;
                   fastcgi_param REQUEST_URI $request_uri;
                   fastcgi_pass unix:/var/run/php-fpm/php-fpm.sock;
            }

    }

    location @au {
            rewrite /au/(.*)$ /au/index.php?/$1 last;
    }

    location ~ \.php$ {
    client_max_body_size 100M;
    proxy_connect_timeout           3600s;
    proxy_send_timeout              3600s;
    proxy_read_timeout          3600s;
    send_timeout                    3600s;
    fastcgi_read_timeout        300s;
    try_files $uri =404;
    fastcgi_pass unix:/var/run/php-fpm/php-fpm.sock;
        fastcgi_index index.php;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        include fastcgi_params;
    }

    location ~ /\.ht {
            deny all;
    }

    location ~ /.well-known {
            allow all;
    }