How do i tune to drop c?

i can't figure it out i have a korg GA-1 tuner and i cant figure it out when i do this it dosn't sound right i press the flat button 4 times for the 6th string and for the rest i press it twice but it dosnt sound right i tried doing it by ear but i just cant do you know any tuners that will tune to drop c or just tell me by ear i need help