How to prepare device to ship to iPhoneATM?

Please be absolutely sure you remove your device from your iCloud account. Instructions for this are located at Apple.
It’s best to restore your devices to factory settings. This is also called data cleared or data wiped.
Congratulations you’re now a certified phone tech!
Phones should be well wrapped so they don’t hit or damage each other. iPhone and other back cameras can actually crack the glass of another phone if they’re compressed together. So always place something between them. When in doubt. Go glass to glass with a divider. It’s always best.