You can block online merchants on your Suyool card through the Suyool app. But for canceling app subscriptions on your iPhone, follow these steps:
Open Settings on your iPhone.
Tap your name at the top.
Select Subscriptions.
Find the subscription you want to cancel and tap it.
Tap Cancel Subscription and confirm.
That's it! Your subscription will be canceled, and no more payments will be made with your Suyool card.
For a visual tutorial, check out this YouTube video: