If you have access to phpMyAdmin, these steps should do the trick:
Step 1: Login to your hosting account and launch myPHPadmin from the
cPanel, or equivalent, to access the WordPress database engine.Step 2: Enter a select SQL command to list all the meta keys you want
to remove. In this example, I want to find and eventually remove the
meta key dcssb_short_url.SELECT * FROM 'wp_postmeta' where 'meta_key' = 'dcssb_short_url'Step 3: Once you are satisfied you’ve narrowed down the selection,
issue a delete SQL command to remove the rogue dataDELETE * FROM 'wp-postmeta' WHERE 'meta_key' = 'dcssb_short_url'Step 4: Issue the same select SQL command again, to verify all the
offending records have been deleted.SELECT * FROM 'wp_postmeta' where 'meta_key' = 'dcssb_short_url'If you get no results returned, it means that you successfully deleted
the records.