Chosen Solution

I ordered the replacement SSD for my MacBook Air from early 2015, and the notice in the package for the SSD says to ensure that MacOS 10.13 High Sierra or later has already been installed so that an EFI Firmware update has taken place. The MacBook is dead and won’t boot, and Apple Support ran many diagnostics and ended up saying that the HDD (SSD) was dead. So:

  1. How can I ensure that the EFI firmware has been previously installed (or install it now) so that it will recognize the new replacement SSD?
  2. What else do I need to do to replace the SSD?

You’ll need an external drive USB thumb drive will do. You’ll need to remove the internal SSD drive following this guide MacBook Air 13" Early 2015 SSD Replacement with the SSD removed turn the system over on your desk (make sure its clean of anything) Now plug in your USB thumb drive and restart your system and press Command (⌘) and R keys to get to the recovery screen, now launch Disk Utility to format your USB drive GUID with a Journaled file system. Once that’s done, just to the OS installer and run it to install the OS onto your drive. During the process the installer will update the systems firmware. Apple has altered things with the intro of Big Sur so be aware you may not get to High Sierra or newer as we once could. Once the install is complete let us know what your OS is so we can then guide you to the next steps. Reference: About macOS Recovery on Intel-based Mac computers