You can also quickly delete all WordPress comments using MySQL or phpMyAdmin. This method is only recommended for more advanced users.
Login to the cPanel dashboard of your WordPress hosting account. Under the database section, click on phpMyAdmin.

Inside phpMyAdmin, you will need to locate your WordPress database. You will see a page like this showing all your WordPress database tables.

Check the box next to wpprefix_comments and wpprefix_commentmeta table.

The name of your comments tables may differ depending on the table prefix you choose during your WordPress installation.

After selecting the comments table, locate the ‘With selected:’ drop-down menu below the table list and select ‘Empty’ from the drop-down menu.
PhpMyAdmin will now show you a warning asking if you really want to empty those tables.

That’s all, we hope this article helped you learn how to easily delete all comments in WordPress.