how do i access icloud on an old iphone 3 with 2 sep verification

I have an old iphone 3 that I want to use as a music player for my granddaughter. When I sign into icloud it asks for a recovery key which I don't have. It send a 6 digit code to my phone but there isn't a popup screen that comes up on the old phone. It won't let me sign into my account. If I go to itunes on my computer with the old phone connected it doesn't list the phone so I can't do anything there either. there has to be a workaround