MacBook Air stuck in Black screen

Water damage is pretty serious, it interferes with electrical activity and causes corrosion, no doubt these have occurred and are why your Mac is not functioning. There are no key combinations or commands to remove water damage; I think your only option is to take it in for service. If it is a fairly recent purchase, the Apple Store may offer to repair it; some accidental damage might be covered if you have AppleCare+ but otherwise you will be looking at an expensive repair. They won't take the computer apart and dry out each integrated circuit or replace damaged elements; instead likely the entire primary board and maybe keyboard will need to be replaced. This type of repair can easily exceed 50% of the cost of a new computer, unfortunately.

If your Mac is older, you can take it to an Apple Authorized Service Provider (they can be located on the Apple web site); they have more flexibility about what they are willing to repair and sometimes will offer to do so for a lower price.