You can change your subscriptions by going to:
https://apps.apple.com/account/subscriptions

This link works on your iPhone, iPad or Mac.

We've also added a shortcut in MealPrepPro to manage subscriptions:

1. Tap Profile
2. Scroll to Subscription
3. Tap Manage Subscription
4. Tap View, change or cancel your subscription

Apple have a guide to managing your subscriptions:
https://support.apple.com/en-us/HT202039