Step 1: Navigate to Appearance >> Customize >> Footer
Step 2: Here you have 4 options to set the Footer: Style, Spacing, Border and Background.
Note: If you have imported the demo, you will not be able to see the changes you made because the page already had a fixed footer style. Please choose a random page for example: Blog page to test it.
Step 3: Click Publish to save the change.
Note: The Footer Style in specific Page Settings take priority over the Default Footer.