In case you wish to use your phpBB 2 application with another domain, you should change the server_name option in your phpBB database. You can do this using the phpMyAdmin tool available in your cPanel.

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.