duplicate in RSS feed

hi,

I have an RSS feed (https://anatomyofamovie.com/category/anatomy-movies/feed/) that goes to itunes (https://itunes.apple.com/us/podcast/anatomy-of-a-movie/id730241106?mt=2)

however on itunes some of my episodes posted are missing. i emailed support at itunes and this was their response:

It appears the same <guid> is being used for the missing episodes including The Hunger Games: Catching Fire. The iTunes Store will only display the latest episode if duplicate <guid> tags are used for multiple episodes.
Please update the <guid> on four episodes that are not appearing in the iTunes Store.

Can anyone help to resolve the duplicates?

PS: Using Powerpress Plugin to create RSS feed.