So you've decided to try a free trial of Wallet Premium, great decision! Your trial will end after 14 days, at which time your Wallet app will become Premium, and you will be charged the appropriate price for a yearly Premium plan (formerly known as the Master plan) for your region.
You can cancel this through:
GPlay app or Google Play Store account if purchased via GP, under the Main Menu > Subscriptions > Wallet trial> Cancel Subscription.
To view your list of subscriptions, you can follow this link:
or Apple Store if purchased through iTunes/App Store https://support.apple.com/en-us/HT202039
You must cancel BEFORE your trial ends to not be charged for Premium.
*Please note, Wallet's free trial allows unlimited bank-connected accounts and Group Sharing!