my F12 key is not turning up my volume on my macbook air

Have you tried the following:

1. Reset SMC by following the directions applicable to your MacBook here ➔ How to Reset SMC. If that does not solve things then-
2. Reset NVRAM/PRAM by following the directions applicable to your MacBook here ➔ How to Reset NVRAM/PRAM.

Axel F.

Can you double check one setting please?

Open System Preferences ➔ Keyboard ➔ Keyboard Tab - Ensure that Use F1, F2, etc. keys as standard function keys is NOT checked. See image below.

If that option (shown in the image above) is checked then UNCHECK it and see whether that solves the issue.

Axel F.