Look for the Optimus icon in your menu bar (top-right of your screen). That's where everything lives — click it any time to open Setup, change settings, or quit.
First-run only: when you click the menu-bar icon, the Setup window opens for you to paste your Deepgram API key. Free 200 dollar credit at console.deepgram.com/signup — the key stays on your Mac, Optimus never sees it.