that app is an SA, which means it's a Supporting Add-on. Thus you won't find a UI to use. As the decription says:
"SA-Investigator is an extension that integrates with Splunk Enterprise Security. It provides a set of views based on the asset, identity or file/process values. Tabs for individual data models like malware, network traffic, certificates are set up for easy viewing and allow the analyst to pivot between these views on a entities without having to open multiple dashboards and enter in criteria to start a search. Workflow actions that allow pivoting from Incident Review are also included." - so you'll find the content in ES.