How to edit Footer area?

On Appearance > Customize > Header and Footer panel there is a Footer Page field, and there you can see which page was selected as template page for footer.

This option enables you to have static page and use it as a footer template for all pages.  All pages inherit settings, elements and shortcodes of the page referenced via this option.

In order to change elements in footer, please locate this page (on all pages list) and edit it.

*Note that the screenshot is from Nifty theme, but the process is the same on all themes.