You can adjust your bid by Ad Group for your Yahoo Gemini Campaigns within the Brax interface.
Navigate to the Campaign Manager screen for the campaign you wish to adjust the CPC for and click on the Ad Groups tab.
In-line edit the CPC by clicking on the blue text in the CPC column. Enter the new CPC amount and click on the check box to confirm the change.
You can also Add Additional Yahoo Ad Groups from here by clicking New Yahoo Ad Group.