Edit /etc/nginx/sites-available/example.com
and add the rules there. Restart/Reload NGINX to push the configuration changes live.
The plugin should work even without these codes because the rules you provided are to exclude Robots.txt and Sitemap files from Cloudflare's Cache Everything Rule.
I use this plugin for client sites and it is how the Site Configuration looks like:
server {
server_name example.com www.example.com;
error_log /var/log/nginx/example.com.error.log;
root /var/www/example.com/htdocs;
index index.php index.html index.htm;
location ~* \.(xml)$ { expires -1; }
location /robots.txt { expires -1; }
include common/php74.conf;
include common/wpcommon-php74.conf;
include common/locations-wo.conf;
include /var/www/example.com/conf/nginx/*.conf;
}