The answer to 'how to fix dimmer switch' is to first turn off the power to the switch at the circuit breaker. Then, remove the switch from the wall and inspect the wiring connections. Tighten any loose connections and check for any damaged or frayed wires. If the switch itself is faulty, you'll need to replace it with a new one. Be sure to turn the power back on and test the new switch to ensure it's working properly.
Fixing a dimmer switch is a relatively simple DIY task, but if you're not comfortable working with electrical wiring, it's best to call in a licensed electrician to handle the repair. They can safely diagnose and fix the issue, and ensure your home's electrical system is up to code.