Database Selecting For Gii

Hi, im new in yii and it is explained that(in the yi book) the code generator gii will generate from tables of "selected database". Well it has selected wrong database, how should i select the one that i want? please help im stuck in this part!

In the model generator form, click on "db" under Database Connection and you can change this to point to another db connection specified in your main.php config file

oh, thanks a lot.