Recent Posts FlexSlider – set different image

I’m using the recent posts flexslider but I was wondering is there’s a way to use a custom image per page.
My featered images wont vertically center, and sometimes it just doesn’t work out to have my featered image as my slider image.

I spend a lot of time trying to make this slider work so I don’t really wanna look for a new one, I just wanna be able to choose the images

https://ww.wp.xz.cn/plugins/recent-posts-flexslider/