The subscription is managed by Apple. You can view subscriptions following the below steps:

  1. Open the Settings app.
  2. Tap your name. 
  3. Tap Subscriptions. (If you don't see "Subscriptions" tap "iTunes & App Store" instead. Then tap your Apple ID, tap View Apple ID, sign in, scroll down to Subscriptions, and tap Subscriptions.)
  4. Tap the DrawingPad - subscription that you want to manage.
  5. It will display all information about available subscription plans and active subscription plan (if any) for DrawingApp.

Alternatively, you can tap here to open the app on iOS to learn more.