I am working on a legacy application and one of the view has degraded performance. I have to fix it,
but the query execution makes me mad as it is a very lengthy plan. Is there an alternative way to understand the plan?
Yes download the free SQL Sentry Plan Explorer tool. There is a paid version too, but the free version is likely sufficient.
Sorry I missed to inform no Third party tools allowed to install in the environment
You are out of luck then. The software gets installed on your own desktop, not on the database server. If a company doesn't allow any software to be installed on your desktop, I don't see how they expect you to do your job. I use so many tools and can't effectively work without them.