It depends on how you subscribed to a paid plan.
I signed up through apply in app subscriptions
If you signed up through Apple In app subscriptions, you will have to cancel through Apple. This can be done right from your device. For more information visits https://support.apple.com/en-us/HT202039
I signed up on the Waitly Website.
This can be down under the setting menu in the upper right corner, Choose profile and look for the "Subscription details" section.