The answer to 'how to fix evaporator coil' is to first turn off power to the HVAC system, then carefully remove the coil and clean it thoroughly. This involves flushing the coil with a coil cleaner solution and using a soft brush to remove any debris or buildup. Once the coil is clean, you'll need to check for any leaks or damage and repair or replace the coil as needed.
It's important to take safety precautions when working with HVAC equipment, such as wearing gloves and eye protection. Fixing an evaporator coil may require specialized tools and knowledge, so it's often best to call in a professional HVAC technician, especially if the coil is difficult to access or the issue is more complex.