If you subscribed on Alexa, you can cancel by saying “Alexa, tell Luminary to cancel my subscription.” After this, Amazon will not auto renew your subscription at the end of your current billing cycle. You will retain access to Luminary Originals until the end of your current billing cycle.
If you signed up for a Luminary via web, iOS, or Android, you must cancel on whatever platform you used to sign up originally. You can find instructions for these other platforms here: How do I cancel my Luminary subscription?