The answer to 'how to fix ductless system' is to first identify the problem with your ductless HVAC system. Common issues include refrigerant leaks, electrical problems, and clogged air filters. Once you've diagnosed the issue, you can take steps to address it, such as repairing leaks, cleaning or replacing the air filter, or resetting the system's electrical components.
If the problem is more complex, such as a compressor failure or major refrigerant leak, it's best to call a professional HVAC technician. They have the expertise and specialized tools to properly diagnose and repair ductless systems. Attempting complex repairs on your own can be dangerous and may even void the manufacturer's warranty.