Permalinks 404 after Subdirectory to Root Migration

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Please use this query in your Database using PhpMyAdmin

UPDATE wp_options SET option_value = REPLACE(option_value, 'oldsite.com', 'newsite.com');
UPDATE wp_postmeta SET meta_value = REPLACE(meta_value, 'oldsite.com', 'newsite.com');
UPDATE wp_posts SET post_content = REPLACE(post_content, 'oldsite.com', 'newsite.com');
UPDATE wp_posts SET post_excerpt = REPLACE(post_excerpt, 'oldsite.com', 'newsite.com');
UPDATE wp_posts SET guid = REPLACE(guid, 'oldsite.com', 'newsite.com');

This will change all your URL’s to new ones.