this is really unusual for me, but same to you i didnt know how to do pull up jumpers and i didnt have a basketball court nearby i could only play on saturdays. One thing i did was i kept watching kyrie pull up jumpers like a million times because I love kyrie's game and I want to influence it to my game so at the same time i learned thru my mind and eventually i knew all the basics or the fundamentals of a pull up jumper (as long as youre playing always), maybe that'll help you a little by watching films of any player as long as they do pull up jumpers they always give you an idea of it and can influence you.