userpoints reset for drupal 7
There is D7 patch if you're savvy enough with that. I wouldn't bother with it unless you anticipate reseting frequently. An easier fix is to just truncate all the tables that store the data:

db_query('TRUNCATE {userpoints}');
db_query('TRUNCATE {userpoints_txn}');
db_query('TRUNCATE {userpoints_total}');