Can't Manage a Report

Report server was installed, set up, and reports published before I got hired, everyone who had a part in this is no longer with my company. At this point I'm responsible for managing the server, but have run into an issue where I don't have any ability to manage one of the reports. I'm not sure how to access the site as an admin or assign myself that role. This is what I see when I click on the three dots on the dashboard. 

Any idea how I can get permissions to manage this report?