To reset the password for phpBB3 all you need to do is the following:

1) Upload to your hosting phpminadmin. This is a simple script that allows you to run a database query on your site allowing you to reset your password. You can download it from http://phpminiadmin.sourceforge.net/

2) You need to get database logins for your phpbb3 database. You can find them by viewing config.php file. Values that are needed are: $dbhost, $dbname, $dbuser, $dbpasswd.

3) Open the phpminiadmin file and update the values there in the following locations:
‘user’=>”database-user-here“,#required
‘pwd’=>”database-user-password-here“, #required
‘db’=>”database-name-here“, #default DB, optional
‘host’=>”",#optional

4) Upload phpminiadmin file to where you have your phpBB3 form is running.

5) Run the script and load the table called “phpbb_users”. Run the following query when you view the table:
UPDATE phpbb_users SET user_email= “youremail@yourdomain.com” WHERE username=”admin”

6) Now go to the login page on phpBB3 and click on “I forgot my password”. Put in your email address and user name. phpBB will send you a link to reset the password and you will be back in business.

Also see our post on how to reset password of wordpress.