Remove an App

I'm using Mojave 10.14.6 and have installed Cold Turkey Blocker. I wish to remove this app but each attempt I make using Force Quit to do so it comes back in the Force Quit window. The instructions explain how to shut your Mac down but not how to remove the unwanted app after doing so. I can't move it to the trash because it says the app is open and there is no way to close the app that I can see. Any suggestions?