The gspot is not a myth LMAO.
But truthfully, every girl's special spot is in a different spot. A good guide would be stick your fingers in about 2 to 2 1/2 inches deep curl your fingers up towards her tummy and vibrate. There is a good starting point.
I have had many experiences with girls... through threesomes and on my own. So, I can tell you it may be in a different spot but you will know when you find it. Also while you have your fingers inside, if you push down lightly on her lower stomach it will make it easier for you to stimulate it.
Good luck