Do you mean stopping a command that's already running, so you can start a new instance of it?
The "Stop Another Command" action can stop a given command, however it will stop all instances of that command, so if you use it in the command you're stopping, the command will stop itself as well.
To get around that, you'd need to use a "launcher" command, which then in turn starts another command that actually does the work, so that the "launcher" command can stop all instances of the worker command, before launching a new instance of the worker command.
Otherwise, if you just want to make sure only one instance of a command is running at a time (while still allowing the command to be used multiple times, just not simultaneously), you can use the "Do not execute this command if it is already running" option (found by clicking the "Advanced" button)