If you are providing a RSS feed, it is easy to display a RSS icon in the frontend on the top right. You have nothing to but to enter the page id of the rss feed at
Constant Editor > Category [START - PAGES] > RSS
How to provide a RSS feed?¶
If you want know, how to provide a RSS feed, please refer to the sample in the manual of the Organiser (ext:org).
See: Administrators > Best Practice > RSS feeds Tag @ https://docs.typo3.org/typo3cms/extensions/org/