If not then you will need to look in your phpbb_users table and find the account details for the person you want to add, then you will need to insert them into the database by running an sql query from phpmyadmin.
the query will look something like this.
INSERT INTO `phpbb_users` VALUES (4,1,'test','ae2b1fca515949e5d54fb22b8ed95575',1160765824,-13,1160757856,1159638537,0,0,'1.00',5,'english','d M Y h:i a',0,0,1160252345,NULL,1,1,0,1,1,1,1,1,1,0,1,0,1,0,NULL,0,'email@address.com','','','','','','','','',NULL,'','',NULL,NULL,'',0,'19680102',0,NULL,NULL,NULL,NULL,NULL,NULL,1,NULL,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,15,5,1,1,1,2,2,1,1,1,1,1,0,7,1,5,1,1,3,3,3,1,1,1,1,1,0,2,'1160271649;4:0',15,NULL,2,0,1160263943,0,0,1,2,0,0,0,0,'0','5','559a7f208866f0063b1ea8d5ca2ee816','cats name',0,0,0,0)
You can also split the database up into smaller section with wordpad, just open the database file and cut and paste in into smaller parts and save them as part1 part2 and so on them run them and sql queries in phpmyadmin this will also help get over the 50Mb limit