Karma - How do I reset karma totals to zero From Online Manual
Currently you need to run a query from phpMyAdmin to reset the karma totals on your forum.
To do so, login to your phpMyAdmin and select your forum database from the left panel and Query from the right panel. In the SQL-query box enter the following query:
UPDATE smf_members SET karmaGood = 0, karmaBad = 0;
UPDATE smf_members SET karma_good = 0, karma_bad = 0;
Replace the prefix 'smf_' with your custom prefix if not using the default.