On Windows, applications have to be in the PATH environment variable so applications can be started without using absolute file path.
Monkey Studio offer an integrated environmeent variable editor which you can customize.
This does not tweak the system environment variable, and only Monkey Studio will use them.
You can customize these variables triggering the 'Edit -> Settings -> Environment variables' menu action.
Feel free to edit and extend the PATH variable, once done this should be immediatly working, if not try restarting Monkey Studio.