Q: I have an iPhone 6s 64GB, randomly turn off when I open an app. And when I tried to use "My Idol" app, the screen freeze.

Double-click the home button on your iPhone & swipe up on the app preview windows to close out of the apps that are causing your iPhone to shutdown/freeze.

After that, restart your iPhone.

If you continue to have issues with specific apps when attempting to open them, go ahead and delete those specific apps and re-download them from the App Store.

You can follow the steps in this article:

If an app you installed unexpectedly quits, stops responding, or won’t open - Apple Support

Download past purchases from iTunes - Apple Support