Using alternative images for 'Presentation' in mobile view

I am using the Presentation feature that is on the Home page of https://hb-themes.com/themes/highend/presentation/ and would like to know what controls I can get over the image when viewing on a Mobile/responsive screen.

Can I change the image used when on mobile?
Can I change how it rescales?
Can I change/override the text colour and background on a specific slide?

My problem is that the images I have used position themselves on mobile in a way that makes text illegible (bright patches on image blanching white text) – so i want to know how to control/influence individual slides.

Thanks