So I looped a trumpet soundfont but when I click on "Remove blank at start" it does absolutely nothing. It's quite annoying, can somebody please help See here for more detail: https://drive.google.com/file/d/1GApHu_FjssARWR3iaRaU2MN-l1uKwawh/view?usp=sharing
That function only works when the beginning contains no sound at all. Probably the part you want to remove contains a very low amount of noise.
However it's still possible to remove that part of your sample and it's very easy. Keep the ALT-button on your keyboard pressed when you drag with the mouse a selection of the part you want to remove. For security Polyphone asks you if you really want to remove it.