How do I transfer my friend's files and storage on her one iPhone7 to her other iPhone7?

My friend has two iPhone 7s and wants to give one as a gift to a friend. The Apple store told her they can't transfer the stuff she has stored on her older 7 to her newer one. She wants to transfer or at least wipe her stuff from the older 7 so she can give it to her friend. If the Apple store can't do this, where does she go to get this done?

On a Mac desktop or laptop you plug the phone in via a USB port, open iTunes and click on the phone icon. It's small but you can find it. I suggest you Google thiIs too.

Itunes on computer. Back up old phone, then upload to new phone, check that it's all there then wipe old phone

It can't be done. If Apple says it can't be done, it can't be done. I guess she could swap the sim cards and maybe that's the only solution.

Yes