Not actually "free" - beware
So, this "free" game automatically signs you up for a 3.99$ a week subscription, with no way to manage or cancel it in-app. Even if you delete it you still get charged.
You have to go to your "Settings", then open "iTunes & App Store". Click on your Apple ID, then "View Apple ID". Scroll down to "Subscriptions: Manage" and turn it off there.
The game might be okay, but tricking people into a weekly subscription with "free" in your name is just plain dishonest.
UltigamerYT about
Piano with Songs, v1.4.3