H is displayed to tell you that the temperature in the fridge has risen above 20 deg C.
You're getting no cooling into your fridge.
This is most likely down to a defrost issue in the freezer. Too much ice has built up and has stopped the airflow into the fridge section. If allowed to continue your freezer will become too warm too.
You need to arrange alternative storage for the food in your freezer.
You can do a full defrost of the fridge, if it's a warm room, 24 hours with the doors open. Then switch it back on again. The fridge and the freezer should both work normally again.
Or if you are handy with a screwdriver then once the freezer is empty remove the back panel in there adn behind that panel is the evaporator. You need to use a hairdryer and melt all the ice in there and then retry it and see how it goes from there.
If however the defrost heater isn't working then the fault will return within a short time.
In this instance you'll need to either have someone come in and repair it or determine which part is causing the problem.
It will be either the pcb, thermistor/thermal fuse or the heater. You need a multimeter to test the heater and thermal fuse to see if faulty.