How do I cancel my SAT or ACT score?

Here’s how to cancel an SAT score.
https://collegereadiness.collegeboard.org/sat/scores/canceling-scores

For the ACT, there is little reason to cancel your test. Instead, as soon as possible, but no later than the Thursday at noon central time after your test, log into the account where you registered for the ACT and remove the names of the universities you listed to receive your test score. You’ll later be able to see the score yourself, but it won’t be reported to universities unless you later decide to send it to particular universities.
If you don’t want the ACT score in your records, you can delete that particular test date. To delete your ACT score for a particular test date, submit a written request. Provide ACT with your name and home address, and ACT will mail you a form to complete and return. ACT will then permanently remove your record for that test date from its files. All scores from that test date will be deleted.
Note: Students may not delete scores used to document participation in State and District Testing.

To receive a form to delete your test score, send your name and address to:

ACT Institutional Services
P.O. Box 168
Iowa City, IA 52243-0168
USA