STM32F4. Internal converter USB-COM problem.

Hi, Gordon, Hi all!
It's me again.
I have some question to community.
STM323F4 includes USB-COM to connect with PC.
But I did not get to use this feature.
Now I'm use external USB-COM converter.
Converter connected to pins {rx:A3,tx:A2}.

My working code:

Serial2.setup(9600, {rx:A3,tx:A2});

Tried to use:

USB.setup(9600);       

and

USB.setup(9600, {dm:A11,dp:A12});

Can I use internal converter? How can I do this?