Thank you for your interest in Bitnami. We only offer the WordPress single-site solution with NGINX. We have the Multi-site solution with APACHE available in all our cloud marketplaces.
If you want to convert the single-site app to the multi-site one, you can follow this guide
Please note that it mentions different changes in the htaccess.conf file that doesn't exist in the NGINX solution. You will need to modify the .htaccess in this case.
You can also follow this guide to install a second WordPress in your current instance but please note that you will need to use a different path to install it as the current installation uses apps/wordpress as installation directory.
Let us know if this solves your question.