Hi @AnweshaPanda,
I think "Variable Stimulus" should fit your needs. You can find it in the bottom left corner of the window.

If it is not visible, it can be enabled from the menu: View → Variable Stimulus.
To create a new Stimulus right click inside "Variable Stimulus" area and select "New...".
In your case it could look like this:

Once it is added you will find your Stimulus in the window shown before. You can start it by double clicking the new item or right click → Run!.
Note: The Stimulus will increase/decrease the variable value at a given time step between 2 consecutive entries (similar to a slope), for a "step" transition you need to pass 2 values with minimal time difference.