To cancel your subscription, you need to go to this link from your iPhone or iPad: https://apps.apple.com/account/subscriptions
Then, you will be able to modify the active subscriptions of your Apple account.
If you are currently subscribed to "Reveals", you should see your subscription listed on this page.
If you need more info about canceling your subscription iOS, please go to this article from Apple support: https://support.apple.com/en-us/HT202039