If you subscribed after August 19, 2021:
Enter the email you used to subscribe.
Click the link in the email you received.
Click Subscriptions and choose "Cancel Subscription". If you're still in the first month/year of your subscription, your subscription may appear under "Trials" instead of "Subscriptions".
If you subscribed before August 19, 2021:
Go to the String Courses Platform: https://courses.string.systems.
Log in.
Click the profile icon on the top right (inside the 3-line menu for mobile).
Choose "Manage subscriptions".
Click "Cancel".