For stock WordPress, this is inside your site’s dashboard (example.com/wp-admin/) head to Settings > General. There you should see the title and description of your site.
If you have an SEO plugin (like Yoast or SEO Framework), then you would need to check inside the settings of the plugin.
Finally, if those don’t work, you may have an issue with your theme. If you have access to the code, check inside the header.php and see what is set inside the <head></head> tags.