Android : Android : I want to remove notification of message

I've made custom message application

so when New message comes, My app works and activity is shown

when i clicked the message button, it shows the list of messages including the new message.

so I want to remove notification of message!

I heard that method cancel() does it.

but I dont know the id of method cancel() about Message Notification.

How can I do it?

public void btnPressed(View view)
{
    badge.hide();
    Intent msgIntent= new Intent(getApplicationContext(),SecureMessagesActivity.class);
    startActivity(msgIntent);

    nm.cancel(0);

}