The heater is located in front of the passenger seat and should be operated after the car is turned off.
Inspection of the waterway part: Generally, the small water tank is blocked. Remove the small water tank, use an air pump to blow it in the forward direction, pour some water in and then blow it, the effect will be better.
If no hot water comes in, check the thermostat and replace it.
Without blowing, check the gear and actual position and air filter.