Design > RSS Feeds Tab Overview
The Design > RSS Feeds Tab is no longer usable in this section of the admin and will be removed soon. We have moved the Blog RSS URL field to the Account > Locations panel and align them with your other social media account URLs.
After opening the Account > Locations tab and clicking Edit, you will be able to input your social media URLs including the one for your RSS Feed.
Check out these blog posts and other help articles pertaining to Design: