First confirm if the head unit has a GPS antenna, and if it is available in the one you bought.
Next, find out which company provides the GPS. As in Pakistan, normally Trakker nav does it. You can get the software from there.
Or you can get a pirated copy, all you need is the software in the SD card.
Once you enter the SD card with the GPS software, just press the GPS Button, and it should work InshAllah:)
Best of luck!