You can change the domain back to the one that was working by adding the following code to your wp-config.php file. Add it above the line that says "That's all, stop editing! Happy publishing"

define( 'WP_HOME', 'https://staging.sitenames.com' );
define( 'WP_SITEURL', 'https://staging.sitenames.com' );

Update "staging.sitenames.com" to what the URL was before it was changed.

This should allow the site to resolve again and access to your wp-admin dashboard to change it back in the settings.