How to active image background on header inside the website ?

Hi, I have purchased the premium version of the Bold photography template. It looks very nice but I don't know how to activate the image background on the header inside the website, as you do for exemple here : https://catchthemes.com/demo/bold-photography-pro/style-guide/image-alignments/ In my website, I have the header title, but I don't succeed to activate the image background : http://leaambroise.com/contact Can you please explain me where I can activate this option? Thank you very much for your help and congrats for your nice work. Nicolas