How to configure phpBB 2 to work with a new domain?
To use your phpBB 2 application with another domain, change the server_name option in your phpBB database. You can do this using the phpMyAdmin tool available in your Site Tools.
Once in phpMyAdmin, select your phpBB database and browse the table phpbb_config (provided that your database prefix is phpbb_). Find the option server_name and change its value to the new domain you wish to use.