drop it in the toilet and give it a flush
rlly tho, take it apart and use a small wet wipe or damp cloth and wipe it down
you could just take it apart and remove the entire PCB (usually held in by one or two screws), place the plastic parts in a mix of warm water and some dish soap, let them sit over night
just remember to let them dry up properly before reassembly
if the PCB has visible residue you can safely use isopropyl alcohol solution with qtips or something to clean it off, just make sure it's not plugged in