Slider Image Help

I bought a theme from a site that won’t help me unless I pay for a subscription again… I believe it’s a simple fix and would love the help.

The site: Life Love & Music

When I set a featured image for my slider on the main page, it looks horrible as a small square. The image for the slider is so wide that it never shows anything good as a small square. What I need is to be able to set one image for the slider (whenever I want a post to be featured) and a secondary image for the small square image.

Here’s the link to the posts I have for the slider on the home page.
https://lifeloveandmusic.net/category/feat-slider

You can see some of the images have pictures to the left of the square and they don’t look good.

Thanks in Advanced.

https://www.ads-software.com/extend/plugins/multiple-post-thumbnails/