You can add the WP_HOME and WP_SITEURL constants in your wp-config.php file to manually override the database options.
Scenario one: You want to surface WordPress from your blog folder.
define('WP_HOME','http://example.com/blog');
define('WP_SITEURL','http://example.com/blog');
Scenario Two: You’ve moved WordPress to another folder, but want it to surface at your root.
define('WP_HOME','http://example.com');
define('WP_SITEURL','http://example.com/blog');
You will need to make sure your index.php file is still in the root, and point the include to the new blog folder.
require('./blog/wp-blog-header.php');
Scenario Three:
If you aren’t comfortable going the wp-config route, move your site back to its original location, login to wp-admin, go to the Settings menu, and adjust the home and site urls in the admin interface.