Iphone locked down in Geogebra App

I have student with an Iphone XR who was using the Geogebra 3D app (geogebra.org) in exam mode on her phone for today's quiz. The app makes the student shut down wifi and enter airplane mode and prevents them from accesses other apps while in exam mode. However, when this student exited exam mode, she was still unable to exit the app. Her phone is frozen on the Geogebra app and she is unable to force it to close. Any suggestions of how she can get the app to close and her phone to work again?