Step 1: Appearance >> Customize >> Footer >> General
Step 2: Choose the Footer style you want.
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: Specific Footer style in the Page Option is more priority than General Footer.