iPhone 6 restore errors at install firmware

I am seeing the connect to iTunes on my iPhone 6 after trying to update to iOS 11.1.1😢

I have followed the advice online at If you see the Connect to iTunes screen on your iPhone, iPad, or iPod touch - Apple Support and the restore extracts software, updates, verifies and then errors (-1) at install firmware...about 2/3rds through.

Can you advise what to do to have the restore complet, at the moment my iPhone is unusable 😟

Regards,

UserfromWarrington