iPhone value missing
I have an iPhone 6s plus that I'm trying to give to my dad. I wanted to reset everything on it to factory settings but i forgot the 6 digit pin and now my phone is disabled for 5 minutes. i don't want to disable it any longer so I found a way to reset it by connecting it to iTunes but as i connect it onto iTunes it says "iTunes could not connect to this iPhone. The value is missing." How can i fix this problem? please and thank you! 🙂
iPhone 6s Plus, iOS 11.2.6