How to edit the footer?

This is the widget area, go to Appearance -> Widgets then edit widgets as needed. If the theme has a background, it can also have other options to setup there: Appearance -> Customize

If the theme has a menu at the bottom it can be set there: Appearance -> Menus then use Footer Menu option to set it up.

You can also use the Classic Widget Editor (not the current block editor) by installing the Classic Widgets plugin: https://wordpress.org/plugins/classic-widgets/