Here is a button which will prompt you for the name of a process to kill, in case you cannot use Task Manager to do the same thing.
For example, type in something.exe when prompted and it will kill the something.exe program if it is running.
When creating the button, set the Function drop-down to MS-DOS Batch Function.
Here is an icon you can use for the button:
Here is the button's command:
@leavedoswindowopen
taskkill /f /im "{dlgstringS|Type in the .exe file exactly... |.exe}"