Q: Need to erase my iPhone 4 for my daughter but my mates Apple ID is still in the phone and he cant remember his password

My friend borrowed my old iPhone4 and set up his Apple ID in it. Now i have it back and want to set it up as an iPod for my 10 year old daughter, trouble is when i try and erase all content and settings it asks for his Apple ID password for which he cant remember and even his email address isn't recognised as an Apple ID anymore. He has a new Apple ID, but this is only since he got his 6s..... Can anybody help with this dilemma...???