Before we get started you will need to make sure Unlimited Elements Plugin is Installed and activated on your website.
Step 1
Navigate to Unlimited Elements >> Background Widgets in the WordPress side menu.

Step 2
Hover over your select background and click install.

Step 3
Inside of an Elementor Page click on a section and in the style tab go to >> Unlimited Backgrounds

Step 4
Under background Type select a background and customize its settings below.

Step by step video tutorial