To begin, navigate to the Toolbar > Edit with Elementor > Footer

Or go to Templates > Theme Builder > Footer > Edit with Elementor. Control the layout, conditions, rules and styles of the footer template. 

How to edit the footer background image?

Click the "Navigator" icon to locate easily the second section of the layout, click on the section, open the Styles tab and edit the image.

Please check these guides for further information:

Create Footers Using Elementor

Guide to Vamtam Elementor Builder