In iGrader, click on the date of the session you would like to modify. You can then scroll through each question (Using the Previous and Next links) and modify the point value for the incorrect and correct responses.
If you've already set up in iClicker preferences that incorrect answers get 2 points and correct answers get 3 points, then you simply need to type the letter of the right answer in the Correct Answer box in iGrader for each question.