Thanks for the reply
As I had mention in my original post, that I want to set/update the Path environment variable on user's (Target) machine where my software in going to installed.
I'm aware of Media -->Path variables
which is only related to build machine and for the install shield environment in which an installer is building. This has nothing to do with Target machine (user's machine).
On the other hand, in install script, I didn't find any method to update the environment varibales on User's machine.
There is one way in Custom actions i.e. using Vb script, but I don't know how to pass the user's selected path (for installation of my product) to this Vb Script so that it can set the env variables there.
Another way (which I am currentley using) is to define the variable and associate it with some component, but during the build process, components are reset (deleted and created again) and so the defined env variable is lost and cannot be created automatically using Automation interface.
Mostly importantly, I want to do this automatically i.e. I don't have to stop the build process just to define this env variable.