Restoring ipohe 6plus to factory setting

Hi

Follow the steps here, including contacting Apple Support or making a Genius Bar reservation if necessary:

If you see the Connect to iTunes screen on your iPhone, iPad, or iPod touch - Apple Support

Note that, for iTunes to be able to connect with a device running iOS 10 or later, your computer must be running iTunes version 12.5.1 or later:

Get the latest version of iTunes - Apple Support

If you want to reset your iPhone to factory settings, try following this: Restore your iPhone, iPad or iPod touch to factory settings - Apple Support

If you already did this, could you describe in more detail what went wrong.

Follow the instructions here:

If you see Error 3194, Error 17, or 'This device isn't eligible for the requested build' in iTunes - Apple Support