The best way to learn is to keep moving forward with new lessons. We don't want you to get stuck doing one lesson over and over again. Practicing with new lessons will keep you interested and motivated. However, if you must repeat a lesson, you can. Simply look for the lesson in the progress bar on your guide page.
Then click on 'Practice this lesson again.' When you repeat a lesson, your scores are added to your overall skill scores on your Performance page.