Open the .pkg (right-click → Open if it says "unidentified developer"). It opens a sign-in window; then grant Screen Recording + Accessibility when asked. Installing also drops Re-register and Uninstall buttons in your Applications folder. To remove it completely: download the uninstaller and double-click it.
These installers aren't code-signed yet, so your OS may warn on first run
(Windows SmartScreen "More info → Run anyway"; macOS right-click → Open;
Android "install unknown apps"). That's expected for a new publisher.