Hi alonso,
We cannot help with full on customizations but I can steer you in the right direction. Basically you’re going to want to modify /wp-content/plugins/events-calendar-pro/views/events-advanced-list-load-widget-display.php – make a copy of that file and put it in an ‘events’ folder in your theme. Then you’ll just need to modify the HTML and PHP to get things looking the way you want. We have a couple tutorials that should help you out too:
https://theeventscalendar.com/how-to-show-featured-thumbnails-in-the-next-events-widget/ (applies to a different widget but shows you how to add the featured thumbnail)
https://theeventscalendar.com/how-to-completely-customize-widgets/ (a little more advanced but shows you how to have even more control over a widget)
I hope that helps but let me know if you have any questions!
– Jonah