On my iPhone 6, I have the iOS 9 Beta.
Today, I tried putting iOS 8.4 on it, and it gives me an error when updating. Now the only thing that comes up on the screen is it telling me to plug my iPhone into my PC and open iTunes. When restarting my iPhone, it just goes straight back to that.
The only other option is to restore my iPhone to factory settings.

/Discuss other Apple problems