For signing in to do the Profile: (the “you” refers to the student)
“Sign-in – If you created a College Board account for the SAT, PSAT or AP, use the same username and password to sign-in. “
And regarding the Profile and making changes…this must be new this year!
“Made a mistake? – If you made a mistake on your application or need to include additional information after you submitted, you can update your application once by clicking “Correct Your CSS Profile” on your Dashboard”