How do I train a specific skill to a specific player?

Hello, how can I select one (maybe a few more) and train their skills up? Like toughness etc?
In the training center when your player has points to allocate click on the player and go into his defensive skills and down tho bottom there is toughness
Does anyone else find that occasionally it doesn't give u the option to train specific skills and only to auto select skills. A few times now when a player has skill points I've gone on to assign them as usual but on his skill screen it shows as if he hasn't got any. Though I will let me auto assign