Open your Linten WordPress theme in a text editor or IDE then open inc/hook/custom.php file, inc and hook is directory/folder. Then find this function linten_footer_copyright and do whatever you want to do. Here’s the file link from WP theme repo –
https://themes.trac.wordpress.org/browser/linten/1.0.6/inc/hook/custom.php#L112
How I found the right file
Let me explain how I found your file.
You gave me this do_action( 'linten_action_footer' ); and it’s an important clue for me to figure the right file. From my 3 years experience, I know that WordPress recommend prefixing almost everything and prefix with theme-slug (in your case the slug is linten). So, I googled with the theme name and found that theme on WordPress theme repository and then downloaded the theme on my computer. Then opened the theme on my code editor and searched for 'linten_action_footer'. From my experience, I also know that do_action() executes an action hook and add_action() registers an action hook. So, I’ve to find something like this add_action( 'linten_action_footer' and I found that. That’s it!
If you’re interested to learn more about action hooks then following links might help you.
https://www.smashingmagazine.com/2016/01/get-started-with-hooks-wordpress/
https://wpshout.com/wordpress-hooks-actions-filters-work/
https://developer.wordpress.org/reference/functions/do_action/
https://developer.wordpress.org/reference/functions/add_action/