On Windows, press Ctrl + Shift + Esc to open Task Manager
Select the unresponsive app
Click End task
On Windows, press Alt + F4 to close the active window
If needed, use Task Manager to force quit
On Mac, press Command + Option + Esc to open Force Quit Applications
Select the app
Click Force Quit
On iPhone or iPad, swipe up from the bottom and pause, or double-click the Home button
Swipe the app away
On Android, open Recent Apps
Swipe the app away
Or go to Settings > Apps > [App] > Force Stop
On Linux, open System Monitor or Task Manager
Select the app
Click End Process or Kill
If the system is frozen, restart the device by holding the power button
Use this only if normal force quit does not work