Clean Text Menu lives in the Mac menu bar, please click on the washing machine icon to have the main window of the app to appear (please look at the image below).

If by chance, you should not see the washing machine icon in the Mac menu bar, please find the app in the Finder (typically inside the Applications folder) and then double click to launch it.

Note that there is an option, which you can activate, to make the app open automatically every time you turn on your Mac. You can find it in the Gear icon menu (in the window toolbar).