On Windows, uninstall CrossFlow from Settings > Apps, like any other application.
On macOS, open "Uninstall CrossFlow", which comes in the same download as the installer, and follow its steps. macOS asks for your administrator password, because CrossFlow is installed for every user of the Mac. The uninstaller uses the standard macOS installer window, so its button still says "Install": that is expected, it only removes CrossFlow. If CrossFlow is still open, the uninstaller closes it. Quit Premiere Pro before you start.
The uninstaller removes the CrossFlow application and its invisible Premiere Pro panel. Your settings, presets, logs and conversion history are kept, so a reinstall picks up where you left off.
To remove those as well, tick Remove CrossFlow User Data in the uninstaller. It is unticked by default because it cannot be undone. It also removes this computer's license activation.
Uninstalling does not free this computer's license slot, even with Remove CrossFlow User Data ticked. If you are moving CrossFlow to another computer, click "Deactivate License" before uninstalling (see Moving your license to another computer). If you already uninstalled, use "Release all computers on this license" from the computer you activate next (see If a computer is lost, broken or sold).