The answer to 'how to fix garbage disposal' is to first unplug the unit and turn off the power. Then, use an Allen wrench to manually turn the blades to clear any jams. Check for and remove any objects that may be stuck in the disposal. If the disposal still doesn't work, you may need to reset the circuit breaker or replace the disposal unit.
It's important to take safety precautions when working on a garbage disposal, such as wearing gloves and turning off the power. If you're not comfortable doing the repairs yourself, it's best to call a professional plumber to service the disposal.