Change background image on Contact form

I purchased the theme a couple of months ago and Im just getting around to working with it.

I want to change the background image on the contact form custom 1. It is currently using the city.jpg file that I see in the media library. I want it to use the businessmen.jpg file that I see in the media library and on contact form custom 3. I search the code in classic mode and did not find city.jpg so it must be hiding somewhere in the css. Did not see it in the page.css so perhaps it is an option somewhere else??

Thanks