You can try and remove the key VERY gently and clean under it. If you do this though, and you damage the white knob sticking up, the entire topcase needs to be replaced, plus whatever else the liquid hit. At an Apple store they likely won't touch it in the store (if you're in the US) and instead ship it out for ~$700 for 13" macs and over $1000 for 15". Water damage is no fun.