How to install macOS back after installing Fedora?
Since you don’t have a recovery partition, the first thing I’d recommend is trying to install macOS from Internet Recovery. 

Your model of MacBook Air should be able to boot directly from an internet connection. First you need to be somewhere where you will be able to access the internet - however this works best with Wi-Fi networks using WEP and WPA security.

Follow these steps:


Ensure your MacBook Air is fully powered off
Hold down the CommandOptionR keys and press the Power button
Keep holding down the keys until you see a spinning globe with the message Starting Internet Recovery
Soon you’ll see a progress bar - be patient as this may take a while
Eventually the OS X Utilities screen will appear
Click Reinstall OS X 
Follow the prompts


If for some reason this doesn’t work, let me know.