You can see your Bend membership in the app, and you manage the billing side through your store. Here's where to find each.
See your membership in the app
Open Bend, go to the Profile tab, and tap Membership.
Manage billing through your store
Changing your plan, updating your payment method, and canceling all happens in your store's Subscriptions section, since Apple and Google handle billing.
On iPhone
Open the App Store, tap your profile picture, tap Subscriptions, then select Bend.
On Android
Open the Play Store, tap your profile picture, tap Payments & subscriptions, tap Subscriptions, then select Bend.