Macbook Air 2015 logic board failure

It depends on how good you are with electronics. The job with replacing these boards is quite easy. But you need to take your time and not to rush. Take note of where all the screws go. Don't be hard when pulling out the motherboard. And when putting the new motherboard, if it feels like it's resisting, check that there's nothing in the way. If your Macbook Air is a 13 inch, the CPU heatsink will be held in place by a screw that goes under the WiFi/BT cable, and you may want to move that cable away first.

You will need two tools. You need a Torx 5 screwdriver to remove the screws that holds the motherboard in place. You also need a Pentalobe size P5 screwdriver to remove the bottom cover. DO NOT even think about using a Torx or anything else. YOU WILL destroy the screws, and it will become a pain to remove the screws even with the proper tools.

While you're at it, buy some good thermal paste like Noctua NT-H1. Your CPU will thank you for it.

Also, Apple doesn't sell replacement parts to ANYONE! They want to charge you a ton of money, and spend weeks replacing it for you. So if you want to do it yourself you'll have to resort to places like Ebay or Aliexpress to get your replacement motherboard that was sourced from some laptop in China, and these usually costs a lot. Make sure the motherboard your buying has the same number as the one you already have. Your motherboard should sit above the CPU or under the SSD. It will say something like 820-00165 or 820-3437. Make sure you get exactly the same number, as a motherboard with a slightly different number might not fit.

Good luck!

Only Apple has parts, so you will need to make an appointment at the Apple Genius Bar for service. If you need to find an Apple Store - Find a Store - Apple.