Perhaps the siteurl or home value got modified when you tried to modify the site URL in WP admin? If so, it might make the front-end and the WP admin inaccessible because it is looking for WordPress in a directory in which it doesn’t exist.
Fixing it in the database
If you have access to the MySQL database, go to the wp_options table and set the siteurl and home values to whatever they were before you edited them (when the site was still working).
Your site should hopefully be back after you make this change. If you edit the site address fields again, you must be very careful you have an understanding of what directory the WP core files are housed in before changing the URL.
Fixing it in WP config
You could also manually override what’s in the database by adding these lines to your wp-config.php. (Change out example.com for your proper site address).
define( 'WP_HOME', 'http://example.com' );
define( 'WP_SITEURL', 'http://example.com' );
But if you did it that way, you’d never be able to edit the Site URL in WP admin again. More info on this here:
https://wordpress.org/support/article/changing-the-site-url/
I’d always be careful when editing those URL fields in WP admin.
Hope that helps; perhaps I misunderstood the question.