depending on which stack are you using that will be your APPNAME. I.e. If you are using WordPress, APPNAME will be wordpress and full path
/opt/bitnami/apps/wordpress/bnconfig if you were using Joomla! then it will be
/opt/bitnami/apps/joomla/bnconfig, and so on.
Above I am assuming that you are using a cloud stack. Could you please confirm that, as well which stack are you using?