Installing Featured Images In RSS
The Featured Images In RSS standard plugin is listed on the WordPress.org plugin directory. This means you can install it to your WordPress website using an "add new plugin" search.
To install Featured Images In RSS Premium you'll need to first upgrade to a Premium license. Then install the Premium plugin .zip file to your WordPress website.
Once the plugin is activated Featured Images In RSS automatically begins working. By default it will look for an image set in "featured image" field on posts.
Next: Use the RSS Image Checker on your feed
Visit the plugin installation guide for step-by-step instructions.