How can I withdraw from the purchase of a course bundle with unlimited access or a course for a year?

The method of withdrawal depends on where the purchase was made:

For purchases on SuperMemo.com using Przelewy24 or PayPal - Refund directly through the contact form or by contacting support@supermemo.com.
Purchase through the Google Play - Refund through the Google platform. You can find more information here.
Purchase through the App Store - Refund through the Apple platform. You can find more information here.

Cancellation