Kunal,
Thank you for asking – hope you and your family are safe as well.
1) About the external tool configuration button, that is the default button, if the bag is not present, it would look the same as the Run button 🙂
You can see a screenshot of the toolbar in this article for instance: https://dzone.com/articles/hide-and-show-eclipse-toolbar
2) Were you able to run your test using the Run button earlier? Or has it never worked? Please provide details on what “unable to run” means – Does nothing happen on click? Does it run, but with an error in the console? Do you see an error dialog? You can share a screenshot as well to explain the problem.
3) Ctrl + Click Run button. This will open the Run configuration dialog. Now find the configuration you want to run and see if there are any errors reported against it.
4) Please send us your entire workspace error log. You can find it at [workspace_location]/.metadata/.log
Thanks!