As far as I know, you need to use Get Processes to create an enumerable, then filter that list to the processes you want to kill and run them through a loop.
If you run a robot server with mutliple users at once, you will need to filter it by current user id. For examples, here is some discussion: Print all processes
And here is the Go submission that came from that if you want an example: https://go.uipath.com/component/killprocessesperuser
Regards.