Depends on what you are looking for
Email Notification for instance if you want all members to yes you will need to do two sql queries since some are saved with a off and others are blank
UPDATE w3t_Users SET U_Notify='On' WHERE U_Notify='Off'
UPDATE w3t_Users SET U_Notify='On' WHERE U_Notify=''
You get the general drift from the command line above This will Update everyone to On so you can send email to all.