Manually delete sent messages

The function delete sent messages doesn´t seem to work. Is there a way to manually delete messages from the database and what command can I use?

It works, switching flag deleted to 1. You can modify the script to delete instead, or delete directly from database using

delete from playsms_tblSMSOutgoing where id = ;

Thanks for your help. It is working so now I can manually delete outgoing posts since the Foxbox interface not working when I try to remove sent messages.