trying to factory reset. no icloud. no itunes on desktop. forgotten restrictions passcode

my friend gave me her daughter's iphone 7 plus. we erased it from the her icloud already. i tried to go to settings and erase all content and data but it asks for a restrictions passcode that she can't remember. she doesn't even remember setting that up. so i tried to do a hard reset through itunes but my itunes on my mac isn't a new enough version to support the iphone 7. or so it says. but its updated as new as it can on the mac that i have. anyway, so i can't do it on my mac and she doesn't have a mac. just an hp that she can't get itunes on. so now i'm stuck. I don't know what to do. how do i factory reset it now?