Hi Andrew,

If you took practice tests, you can reset your progress in those with the following steps:

1. Go to https://www.khanacademy.org/mission/sat/exams
2. Select a practice test you've done
3. Scroll to the bottom of the page
4. Find the "Reset this test" button 
5. Click the button and confirm your reset on the pop-up 

In terms of the skills you already practiced, you can just practice them again - there's no way to reset that progress unless you create a new account.

Hope this helps! Let me know if you have any further questions.
Shadow