Question: How to unlink apps from wrong apple id account
I got my brother an iPad and to make him a surprise I configured it with my apple Id, downloaded some apps to make a draw and let him find it on his desk with my draw on the screen.
Then we configured the iPad with his apple id, deleting mine, but now when the apps that I installed (included keynote and other apple apps) ask for updates, he can't update them since the iPad asks for my account's password.
How to overcome this issue and link those apps to his account, the primary iPad account?
iPad Pro Wi-Fi, iOS 11.1