Add below line in the wp-config.php after database credentials.
define ('WP_ALLOW_REPAIR', 'true');
The next step is to visit the database repair page. You’ll find this at http://your-site.com/wp-admin/maint/repair.php.
You have two options there,
Repair the database & Repair and optimize the database
first option will just repair the datbase tables if there is any issue but better to run second option that will repari aswell optimize the tables for best performance.
You can run this url for twice to make sure the repair process is done.
Make sure you remove the code line in wp-config.php