Change header image from desktop to mobile

Hi,

can somebody give guidelines or the solution of how i can bring inside cover block (Gutenberg based site) a different picture when my site goes to mobile version, removing the first one of desktop pic? I am asking this because my header (inside cover box) although has dimensions of 1600x1200px getting blurred under mobile view.

*i am using proteo theme.

Thank you.

The page I need help with: [log in to see the link]