whistle between my fingers

I actually always wanted to do this and I Think I learned it only last month!
It’s quite easy once you get the hand of it.
the easiest way is to make an O (more like an oval actually) using your thumb and middle finger. Then put it about 1-2cm into your mouth. Push the tip of your tongue back using the two fingers and blow on it. takes a little bit but you should be able to get it pretty soon.