I accidentally spilled coffee on my MacBook Air keyboard, any advice?

Hi,

First of all, you must power off your MacBook Air as soon as possible, then upside down the keyboard on the towel for a while.

And call Apple support to tell them about circumstance you face right now. You would need to make Genius Bar reservation or take your MacBook Air to your local Apple Authorized Service Provider to be examined your MacBook Air there.

Official Apple Support

Genius Bar Reservation and Apple Support Options - Apple

Apple - Find Locations - Location Selector

You should remember that liquid damage to Mac computers and accessories not covered by warranty.

Liquid damage to Mac computers and accessories not covered by warranty - Apple Support