I want a solution for my locked MacBook Air

That machine has a firmware password. If you can't remember it, you will have to take it to Apple or an authorized service provider along with the original proof of purchase from an authorized retailer.

If you don't have that, it's a brick.

If you bought it used, return it and get your money back if you can. If you can't, turn it over to the police as it's likely stolen.

Then your only option is to take it to Apple or an authorized service provider along with the original proof of purchase as I've already stated.

If you can't produce the original proof of purchase, you may as well drop it off at your local electronics recycler. It's useless. There is no way past the firmware passcode. That's what it's for... to make sure no one without the proper passcode can use it at all.