Mostly the controller (receiver) is located in the housing of the ceiling fan.
Disconnect the power for the fan by removing the fuse in the power box and then access the ceiling fan housing.
Be safety aware you will be working with lethal voltage circuits! If there is no separate fuse marked for the fan then perhaps it is connected in with the lights fuse. If the fan was not working at all so that you can’t verify that it has no power connected by trying to turn it on and off after having removed the fuse, then take no chances and operate the house main power isolating switch or remove all the main household side power and light supply fuses in the power box. If in any doubt contact an electrician. It’s not worth doing it yourself, your life is worth more.
You don’t state the make and model but there are normally some screws that can be undone to access the wiring etc.
Here’s the ifixit Ceiling Fan Light Fixture Replacement guide.
The images shown at Step.2 in the guide (hover mouse over right side image) give you a rough idea where to look for the controller.