I have an iphone 4 nobody has used for years. Want to reset it to let my kids play with it as they keep wanting to play with my phone, so may as well let them play with this that has been sitting unused in a box. But it keeps asking for an icloud password for an email address and nobody remembers any password. How do I reset this to factory default, preferably without using a computer, but will if necessary. I thought this should be simple but somehow it's complicated as I already played around in the menus and googled and confused by results.