To back up, restore or optimize a table, click on the appropriate action icon for that table, or select multiple tables and apply that action to all selected by choosing the corresponding action at the top of the screen.
Back up, Restore & Optimize Table Data
NOTE: If your database is very large, you might want to use an independent tool (like mysqldumper or phpMyAdmin) to back up and restore your tables. At least one of these should be available from your site control panel.
Utilities >> Back up, Restore & Optimize Table Data