First thing to do is see if you have access to an admin console like phopMyAdmin. This will make it much easier to change. Then browse the LUM_User table (listed on the left) and edit the records (click the pencil icon) for the user you want to change.
If you don't have access to that, you will probably have to either log in with a shell, or create a PHP file with the command in it, both of which are a bit more complicated, and then run a command like this one:
UPDATE LUM_User
SET CountComments = 0
WHERE Name = 'WallPhone';
Comments
If you don't have access to that, you will probably have to either log in with a shell, or create a PHP file with the command in it, both of which are a bit more complicated, and then run a command like this one:
UPDATE LUM_User SET CountComments = 0 WHERE Name = 'WallPhone';