I should start by saying I sadly have zero understanding of Mac os sadly <.< But it should be downloaded as a zip file. Then export the folder inside onto your desktop or somewhere fitting.
From there I don't think the game shows a client/app to open? Maybe it just doesn't for me with Windows os. It's worth a shot, but did you give this fix a try? (We've had other Mac users have success with this.)
Download fix command: Here
Place "Fix_Permissions.command" file in same folder as "tyranoscript.app" then double click it. (possibly right click or ctrl+click and choose open)
In terminal you need to give the script +X permission to run.