The answer to 'how to fix ductwork' is to inspect, seal, and insulate your ductwork to improve efficiency and prevent air leaks. Start by visually inspecting your ductwork for any cracks, holes, or loose connections. Use a duct sealant or mastic to seal any gaps or leaks you find. You can also add duct insulation to prevent heat loss and improve airflow.
If you have more extensive damage or are unsure how to properly fix your ductwork, it's best to call in an HVAC professional. They can thoroughly inspect your system, identify any issues, and make the necessary repairs to ensure your ductwork is functioning efficiently.