Support for desktop notifications in Phabricator was added long time ago
Bitnami packages and configures already existing applications. We can only offer support and help on basic and most frequent application configurations. Always based on the default configuration or on our guides. If you want to enable these notifications, probably someone with more experience and knowledge about that specific tool can help you better than we can.
We suggest you to post your question on the official support forums of the application so others can help you with your issue.