The answer to 'how to fix dehumidifier' is to first check the air filter and clean or replace it if it's dirty. Next, inspect the water collection bucket and empty it if full. You may also need to check the compressor and condenser coils for debris and clean them. If the dehumidifier is still not working properly, you may need to have a professional HVAC technician diagnose and repair the issue.
Regular maintenance like cleaning the filter and emptying the bucket can help prevent many common dehumidifier problems. However, more complex issues like a malfunctioning compressor or refrigerant leak should be addressed by a qualified HVAC technician for safety and proper repair.