Can I choose gallery thumbnail image?

Hi!
I′m currently testing this awesome gallery plugin. I′m planing to have many galleries displayed by shortcode as: [print_gllr id=1611 display=short]. I′m wondering if I could somehow change the thumbnail image of each gallery? Now it gets chosen by the gallery it self. It seems to pick some image from the end of the image sequence, but not necessarily the very last one. However, if I change the order of my images, the gallery thumbnail image will remain the same. So it is quite impossible to set the image I want to play as thumbnail. Is there maybe some workaround for this, could I add something to the shortcode? Or is this feature maybe available in the pro version?

Thank You so much for any help!

https://www.ads-software.com/plugins/gallery-plugin/