The right way to solve a problem is to go the root of it. In this case, when this car left the factory, it worked just fine with the wiring to the fan just in this way. If, now there is a heating problem, the solution is not to fiddle with the wiring to "make the fan go faster". The problem may be the cap, gasket, thermostat etc.
To give an example, if a person is suffering headache caused by a brain tumour, taking Panadol with fix the headache temporarily but it is the tumour that needs attention. I don't think it is good idea to alter the way the fan works, better to figure out why the car is behaving the way it is.
@mohsiiiin has to list down all possible causes of his problem and work his way down the list, eliminating them one by one starting from the cheapest solution down to the most expensive one.