Jefferson Pro supports Jetpack integration for a number of features. Install it if you have not already.
1. Install the Plugin
Go to Plugins, search for Jetpack - then install and activate it.
You will need to register with wordpress.com (free) and connect your site to the account. Basic Jetpack usage is free.
2. Activate Related Posts
Go to Jetpack > Settings and search for 'related'.
Flick the tab to switch this module on and it will turn blue. Set it up like the screenshot below.
3. Tweak the text within the Customizer
It also adds an extra pane to the Customizer where you can change the heading text. So go to Appearance > Customize > Related Posts.
You'll need to click into a single post first to see the options.