Right click on any sibling leaf to add a new test step "Run Exe":

Define selection time parameters:
Variable Name will be recognizable and its value available in your script.
Default value

Copy the script below and paste it to the template created by the ESL Editor.
The script invokes any WIndows executable file using ESL "Run" functions.
Press F1 in ESL Editor for Help and API index.

To launch any Windows application:
Drag "Run Exe" to the Flow Editor - the "User Parameters" window will pop up
Write in a “Value” the application name in apostrophes, as you write it in the Windows command line. 
Ckick "Run" button to execute.