RSS FEED FOR A PARTICULAR CATEGORY

Are you saying that you want your main RSS (https://www.yoursite.com/feed) to be limited to one category? I’m not sure about modifying the main site feed, but just adding “feed” after the url to the category archive page gives a feed for that category (https://www.yoursite.com/category/wp_help/feed). You can do that for any categories you want an RSS feed for.

This might help: WordPress Feeds