Write the last time food was known cold, first warm reading, door-opening history, power outage, setting change, unusual sounds and any error display. Use a clean appliance thermometer if available and safe, but do not taste food to decide whether it is safe. Follow the linked FDA guidance for U.S. food triage and the local food authority elsewhere.
For service, provide model/serial, age only if known, temperatures in both compartments, whether fans or compressor sounds are intermittent, visible frost location and clearance around the appliance. A technician may evaluate sensors, airflow components, controls, refrigerant or sealed-system operation; the owner should not pierce lines, add refrigerant or work on energized components. Keep the doors closed while arranging food protection and service so the remaining cold air is not lost unnecessarily.