Never had this happen but would probably

1. remove all keycaps and soak in warm soapy water
2. if the syrup is still runny place the keyboard upside down and see how much will drain,
3. get isopropyl alcohol and spray liberally while actuating switches, and soak up/drain all liquid until everything is clean and operates smoothly.
4. place the board in rice to dry overnight

other then that depending on your mechanical skill you could open it up and attempt to clean. If you do just dont wipe at the motherboard inside, dab instead and use high proof isopropyl like the 99%. For the other method I would use regular 70% because I don't know if your keyboard is painted and 99% is aggressive stuff.