Edit footer and copyright
Tutorials for WPKoi themes with template parts
Customize template parts and footer
Some of the footer functions are in the customizer. You can build template parts with blocks.
You can setup some areas in the customizer (Appearance-> Customize).
The premium versions have more functions like paddings, color and typography change etc.
You can change the copyright text with the premium versions also at the customizers General section. With the free themes, You can hide it with some additional CSS code.
Edit footer and other template parts
In the new generation WordPress themes You can edit the template parts in the block based site editor.
Go to Appearance-> Template Parts admin menu and select the template part You want to edit.
If You want to learn more about the block based editor, You can find details at WPBeginner and WordPress.org.