Due to the way the App store works, only you can cancel or change your subscription.You can access your subscription options as follows:
Open Pillow on your iPhone
Tap on the Settings icon on the top right corner
Scroll down to find "Pillow Premium"
Tap on "Manage subscription"
Alternatively:
Open the App Store app on your iPhone or iPad
Tap on the profile button on the top right corner
Select "Manage subscriptions"
A screen should appear allowing you to modify your subscription.