How do you fix a 96 Toyota starlet to blow hot air?

Apart from the obvious, the engine has warmed up. Check that you have the controls set to give heat and vent into the car, there may be a fault with the cooling system.

You may have an air lock in the cooling system to the radiator in the car. In this case, remove the reservoir cap and squeeze the large hoses, to push the air out. Top up the coolant.

The thermostat may be jammed open. Check that the temperature guage shows normal, to confirm this. If the thermostat is prematurely open, the engine will never get up to temperature, heater not work and the car will use more fuel.