I have been hearing things about it and was wondering how to do it.
You can either use flowable which will do that on its own or use RTV and use a spoon to get it concave.
Just lay down the silicone, then use some kind of rounded object (I use my thumb nail) and just scrape off some of the silicone. The steeper the angel, the steeper the concave, the less response.
Thank you.