Bitnami Stacks are self-contained and they include their own web server, their web server, etc. If you want to use your XAMPP and install other applications on top of it, you can use Bitnami Modules. You can find a list of all available modules to run on top of XAMPP in the link below:
However, Dreamfactory is not available to run as a module so you have to install it as a Bitnami Stack.
About the script Online Training Center Manager, where did you get it? We don't provide it.