One of my keys fell off-will apple fix it for free?

Where are you located? If it's something that doesn't require a new part, then an Apple Store will evaluate it for free and might even fix it if it just needs to be place back correctly. I've had certain Apple keyboards where the key was loose, but I was able to pull it completely off and then place it back in the correct alignment. If that's all that's needed, I think an Apple Store would do it for free.

yinghang13 wrote:

I'm located in London.

Fine. Then you should have access to an Apple Store and I would suggest making an appointment. They will always evaluate an issue for free, while Apple's outside service providers might charge a diagnostic fee just to look at a device.

Which model though? There are different keyboard designs, and some are very difficult to fix if a key comes off. Some people have gone in for an evaluation and were essentially told that the only fix was a complete top case replacement since the keyboard is integrated into the case.

There might also be temporary fixes such as using mounting putty, although that can leave a mess if too much is used.

yinghang13 wrote:

I have a macbook air. Will it be fine?

Tough to say without actually seeing it. I understand it's a MacBook Air, but there are different models over the years, and you haven't been specific which one. Some have a more traditional keyboard of the type that Apple used since the 2006 MacBook/MacBook Pro. There have been variations over the years, which is why I'm asking what year.

yinghang13 wrote:

Its the 2015 model.

I think that's kind of tricky. Those are pretty thin and require a keyboard with less key travel. It's really hard to tell without seeing exactly what happened.