To force quit a Mac app, you can call up the Force Quit Applications menu from the Apple menu button in the upper-left corner or by hitting Command-Option-Esc. But if it's a menu bar app that's hanging or otherwise giving you problems, you won't find it listed in the Force Quit window. In such instances, you will need to use Activity Monitor.
Here's what to do:
1. Open Activity Monitor.
2. Find the app listed or search for it using the search bar in the upper-right corner.
3. Click on the app to highlight it.
4. Click the Force a process to quit button, which is located in the upper-left corner and has a stop sign with an X on it.
5. Click the Quit button to quit the app, and if that doesn't do it, follow the same steps and hit the Force Quit button.