Mailchimp RSS FEED

Hi,
My blog posts go out through an RSS Feed from Mailchimp. For the past week, none of my posts have been going out. After speaking with mailchimp for an hour they told me something is wrong with my RSS Feed. I have NO CLUE how to fix it or what is wrong. Can someone please help me? I am not very good at this so if you can walk me through how to fix it like you would explain to a newbie that would be amazing.