I released an app in the app store, and the compatibility information is incorrect. In the deployment info of xcode, I set the devices to iPhone, but in the app store it shows that it's 'Compatible with iPhone, iPad, and iPod touch'.
How do I change the compatibility information to just iPhone?
Don't be confused. That simply means it will run in compatibility 1x/2x mode on iPad.
See 2.4.1 in the ASRGs Hardware Compatibility
Otherwise, there is no simple lever to pull that will make your app iPhone-only and prevent it from running on an iPad.
Apple prefers that devs focus on iOS versions and features, not devices first.