Log in to your Yondo store website at https://videos.bertkinister.com/login. The customer must use the email and password they used when first purchasing the subscription.
From the menu at the top right of the site, choose "Dashboard".
In the column on the left, there's a section called "Video Subscription". If there is an active subscription, a button "Cancel Subscription" is visible.
Click this button and confirm to cancel the subscription.