First check for broken wires or loose connectors around the fan circuit. If no problems were found, your best bet is to replace the entire cooling fan. Call your local repair shop. Every type of vehicle is different.
Separate A/C-System from electrical power. Check if the fan is blocked by foreign parts. If yes, remove parts and check if fan will start to operate regularly. If not, replace the fan by an spare part.
A non Working cooling fan can be fixed by contacting the concerned dealer to send the mechanic for the same if it is branded or under warranty but if it is not branded or does not cover any warranty then it can be taken to the nearest repairing shop.