My dad was following a step by step on how to factory restore his 2015 Macbook Air and must have deleted the OS. When booting up, a folder with a question mark flashes. When booting in recovery mode, it has a globe and is performing an internet recovery. I'm trying to help my dad over the phone but it's a pain in the ass. He did the internet recovery last week but he says he doesn't know what happened after. He thinks the computer just turned off. Any advice?