Installing my Hunter ceiling fan on a previous 3-way switch. The dual switch on the wall runs the existing light(both switches), my house is a new modular and this is how the light works. The red goes into one and they are connected with a black. How do I use one switch for the light and the other switch for the fan?

Describe the wiring, how many cables and what wires are connected to the switches.

What do you mean "previous 3-way switch"?

Are you talking about two switches on opposite sides of the room that control the same thing, or two switches right next to each other that both control wires in the same junction box?

Ceiling Fan Wiring, Ceiling Fan Wiring Technical Help, Do it Yourself (DIY) - Ceiling Fans N More