how long will it take for training will take affect of said player?

I have been playing FM for almost 9 months now and love using the training players and making the most of all the coaches, but I need to sort out a player who keeps on shooting from 40 yards and missing 9 times out of 10. I'm really out of my depth here but I keep asking my first team coach for him to stop shooting from way off the opponents box, but nothing is stopping him. I could either try and sell him and maybe getting someone who will follow orders or try and ask him myself to stop it.

First port of call would be your tactics.

Give him passing options and he won't end up shooting all the time.