In order to cancel or edit your YouTube Creator Subscription, go to Account settings > Profile and click on Edit Subscription. At the bottom of the Edit Subscription page, click on Cancel your YouTube Creator Subscription. Note that your subscription is not cancelled until you have gone through these steps.
If you cancel during a free trial, any videos uploaded with Epidemic Sound music after the cancellation date will be monetised. If you cancel during a billing period you can continue to use Epidemic Sound's music in videos that you upload before the last date of your current billing period.