Subscriptions to the Vi Trainer app are managed through either your iTunes App Store or Google Play Store account. Any adjustments or cancellations will need to made directly through that account.
On your iPhone:
1. Go to Settings > [your name] > iTunes & App Store.
2. Tap your Apple ID at the top of the screen.
3. Tap "View Apple ID". You might need to authenticate your Apple ID
4. Tap Subscriptions > Vi Trainer
5. From here you can adjust your plan or cancel your subscription
Google Play account:
On your Android phone:
1. Open the Google Play Store
2. Tap Menu > Account > Subscriptions
3. Locate Vi Trainer and click on it
4. From here you can adjust your plan or cancel your subscription