Limiting Description Text on a Blog Post of a (Default) Theme

I have WP RSS Aggregator activited and the configured feeds are indeed showing up on the front-end Divi ‘Extra’ page ‘out of the box’. However, the description text is NOT a summary. Instead, I want a 50 word summary and then a ‘Read More’ (or something like that where they can click and read the entire blog post. Where in the settings of the Extra or the RSS Aggregator is that setting set?